From log:

{"Protocol":0,"Id":"2429f791cc97cf0bff4839634ccca224","Path":"/media/nas/Serije/Earth Final Conflict - Season 1-5 (All seasons)/Earth Final Conflict - Season 1/EFC 0101 - Decision.avi","EncoderPath":null,"EncoderProtocol":null,"Type":0,"Container":"avi","Size":366946304,"Name":"EFC 0101 - Decision","IsRemote":false,"ETag":"fd7ebe2f84f7e5a7a309f9fba43c4e74","RunTimeTicks":24982399999,"ReadAtNativeFramerate":false,"IgnoreDts":false,"IgnoreIndex":false,"GenPtsInput":false,"SupportsTranscoding":true,"SupportsDirectStream":true,"SupportsDirectPlay":true,"IsInfiniteStream":false,"UseMostCompatibleTranscodingProfile":false,"RequiresOpening":false,"OpenToken":null,"RequiresClosing":false,"LiveStreamId":null,"BufferMs":null,"RequiresLooping":false,"SupportsProbing":true,"VideoType":0,"IsoType":null,"Video3DFormat":null,"MediaStreams":[{"Codec":"subrip","CodecTag":null,"Language":null,"ColorRange":null,"ColorSpace":null,"ColorTransfer":null,"ColorPrimaries":null,"DvVersionMajor":null,"DvVersionMinor":null,"DvProfile":null,"DvLevel":null,"RpuPresentFlag":null,"ElPresentFlag":null,"BlPresentFlag":null,"DvBlSignalCompatibilityId":null,"Rotation":null,"Comment":null,"TimeBase":"1/1000","CodecTimeBase":null,"Title":null,"Hdr10PlusPresentFlag":null,"VideoRange":0,"VideoRangeType":0,"VideoDoViTitle":null,"AudioSpatialFormat":0,"LocalizedUndefined":"Undefined","LocalizedDefault":"Default","LocalizedForced":"Forced","LocalizedExternal":"External","LocalizedHearingImpaired":"Hearing Impaired","DisplayTitle":"Undefined - SUBRIP - External","NalLengthSize":null,"IsInterlaced":false,"IsAVC":false,"ChannelLayout":null,"BitRate":null,"BitDepth":null,"RefFrames":null,"PacketLength":null,"Channels":null,"SampleRate":null,"IsDefault":false,"IsForced":false,"IsHearingImpaired":false,"Height":0,"Width":0,"AverageFrameRate":null,"RealFrameRate":null,"ReferenceFrameRate":null,"Profile":null,"Type":2,"AspectRatio":null,"Index":0,"Score":null,"IsExternal":true,"DeliveryMethod":null,"DeliveryUrl":null,"IsExternalUrl":null,"IsTextSubtitleStream":true,"SupportsExternalStream":true,"Path":"/media/nas/Serije/Earth Final Conflict - Season 1-5 (All seasons)/Earth Final Conflict - Season 1/EFC 0101 - Decision.srt","PixelFormat":null,"Level":0,"IsAnamorphic":null},{"Codec":"mpeg4","CodecTag":"XVID","Language":null,"ColorRange":null,"ColorSpace":null,"ColorTransfer":null,"ColorPrimaries":null,"DvVersionMajor":null,"DvVersionMinor":null,"DvProfile":null,"DvLevel":null,"RpuPresentFlag":null,"ElPresentFlag":null,"BlPresentFlag":null,"DvBlSignalCompatibilityId":null,"Rotation":null,"Comment":null,"TimeBase":"1/25","CodecTimeBase":null,"Title":null,"Hdr10PlusPresentFlag":null,"VideoRange":1,"VideoRangeType":1,"VideoDoViTitle":null,"AudioSpatialFormat":0,"LocalizedUndefined":null,"LocalizedDefault":null,"LocalizedForced":null,"LocalizedExternal":null,"LocalizedHearingImpaired":null,"DisplayTitle":"384p MPEG4 SDR","NalLengthSize":null,"IsInterlaced":false,"IsAVC":false,"ChannelLayout":null,"BitRate":1033051,"BitDepth":8,"RefFrames":1,"PacketLength":null,"Channels":null,"SampleRate":null,"IsDefault":false,"IsForced":false,"IsHearingImpaired":false,"Height":384,"Width":512,"AverageFrameRate":25,"RealFrameRate":25,"ReferenceFrameRate":25,"Profile":"Advanced Simple Profile","Type":1,"AspectRatio":"4:3","Index":1,"Score":null,"IsExternal":false,"DeliveryMethod":null,"DeliveryUrl":null,"IsExternalUrl":null,"IsTextSubtitleStream":false,"SupportsExternalStream":false,"Path":null,"PixelFormat":"yuv420p","Level":5,"IsAnamorphic":false},{"Codec":"mp3","CodecTag":null,"Language":null,"ColorRange":null,"ColorSpace":null,"ColorTransfer":null,"ColorPrimaries":null,"DvVersionMajor":null,"DvVersionMinor":null,"DvProfile":null,"DvLevel":null,"RpuPresentFlag":null,"ElPresentFlag":null,"BlPresentFlag":null,"DvBlSignalCompatibilityId":null,"Rotation":null,"Comment":null,"TimeBase":"3/125","CodecTimeBase":null,"Title":null,"Hdr10PlusPresentFlag":null,"VideoRange":0,"VideoRangeType":0,"VideoDoViTitle":null,"AudioSpatialFormat":0,"LocalizedUndefined":null,"LocalizedDefault":"Default","LocalizedForced":null,"LocalizedExternal":"External","LocalizedHearingImpaired":null,"DisplayTitle":"MP3 - Stereo","NalLengthSize":null,"IsInterlaced":false,"IsAVC":false,"ChannelLayout":"stereo","BitRate":129128,"BitDepth":null,"RefFrames":null,"PacketLength":null,"Channels":2,"SampleRate":48000,"IsDefault":false,"IsForced":false,"IsHearingImpaired":false,"Height":null,"Width":null,"AverageFrameRate":null,"RealFrameRate":null,"ReferenceFrameRate":null,"Profile":null,"Type":0,"AspectRatio":null,"Index":2,"Score":null,"IsExternal":false,"DeliveryMethod":null,"DeliveryUrl":null,"IsExternalUrl":null,"IsTextSubtitleStream":false,"SupportsExternalStream":false,"Path":null,"PixelFormat":null,"Level":0,"IsAnamorphic":null}],"MediaAttachments":[],"Formats":[],"Bitrate":1175055,"FallbackMaxStreamingBitrate":null,"Timestamp":null,"RequiredHttpHeaders":{},"TranscodingUrl":null,"TranscodingSubProtocol":0,"TranscodingContainer":null,"AnalyzeDurationMs":null,"DefaultAudioStreamIndex":null,"DefaultSubtitleStreamIndex":null,"HasSegments":false}

/usr/lib/jellyfin-ffmpeg/ffmpeg -analyzeduration 200M -probesize 1G -fflags +genpts -f avi  -i file:"/media/nas/Serije/Earth Final Conflict - Season 1-5 (All seasons)/Earth Final Conflict - Season 1/EFC 0101 - Decision.avi" -map 0:0 -map 0:1 -codec:v:0 copy -map_metadata -1 -map_chapters -1 -threads 0 -codec:a:0 copy -y "/cache/transcodes/8482e5b6fef2ff285cb9e90d65f5c832.avi"


ffmpeg version 7.1.3-Jellyfin Copyright (c) 2000-2025 the FFmpeg developers
  built with gcc 14 (Debian 14.2.0-19)
  configuration: --prefix=/usr/lib/jellyfin-ffmpeg --target-os=linux --extra-version=Jellyfin --disable-doc --disable-ffplay --disable-static --disable-libxcb --disable-sdl2 --disable-xlib --enable-lto=auto --enable-gpl --enable-version3 --enable-shared --enable-gmp --enable-gnutls --enable-chromaprint --enable-opencl --enable-libdrm --enable-libxml2 --enable-libass --enable-libfreetype --enable-libfribidi --enable-libfontconfig --enable-libharfbuzz --enable-libbluray --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libopenmpt --enable-libdav1d --enable-libsvtav1 --enable-libwebp --enable-libvpx --enable-libx264 --enable-libx265 --enable-libzvbi --enable-libzimg --enable-libfdk-aac --arch=arm64 --cross-prefix=/usr/bin/aarch64-linux-gnu- --toolchain=hardened --enable-cross-compile --enable-rkmpp --enable-rkrga --enable-ffnvcodec --enable-cuda --enable-cuda-llvm --enable-cuvid --enable-nvdec --enable-nvenc
  libavutil      59. 39.100 / 59. 39.100
  libavcodec     61. 19.101 / 61. 19.101
  libavformat    61.  7.100 / 61.  7.100
  libavdevice    61.  3.100 / 61.  3.100
  libavfilter    10.  4.100 / 10.  4.100
  libswscale      8.  3.100 /  8.  3.100
  libswresample   5.  3.100 /  5.  3.100
  libpostproc    58.  3.100 / 58.  3.100
Input #0, avi, from 'file:/media/nas/Serije/Earth Final Conflict - Season 1-5 (All seasons)/Earth Final Conflict - Season 1/EFC 0101 - Decision.avi':
  Metadata:
    software        : VirtualDubMod 1.5.10.2 (build 2540/release)
  Duration: 00:41:38.24, start: 0.000000, bitrate: 1175 kb/s
  Stream #0:0: Video: mpeg4 (Advanced Simple Profile) (XVID / 0x44495658), yuv420p, 512x384 [SAR 1:1 DAR 4:3], 1033 kb/s, 25 fps, 25 tbr, 25 tbn
  Stream #0:1: Audio: mp3 (mp3float) (U[0][0][0] / 0x0055), 48000 Hz, stereo, fltp, 129 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Output #0, avi, to '/cache/transcodes/8482e5b6fef2ff285cb9e90d65f5c832.avi':
  Metadata:
    ISFT            : Lavf61.7.100
  Stream #0:0: Video: mpeg4 (Advanced Simple Profile) (XVID / 0x44495658), yuv420p, 512x384 [SAR 1:1 DAR 4:3], q=2-31, 1033 kb/s, 25 fps, 25 tbr, 25 tbn
  Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, fltp, 129 kb/s
Press [q] to stop, [?] for help
frame= 8048 fps=0.0 q=-1.0 size=   67072KiB time=00:05:21.92 bitrate=1706.8kbits/s speed= 643x    
frame=11620 fps=11591 q=-1.0 size=   88832KiB time=00:07:44.84 bitrate=1565.5kbits/s speed= 464x    

[q] command received. Exiting.

[out#0/avi @ 0x7fa999d400] video:101462KiB audio:8879KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 0.820445%
frame=14262 fps=9437 q=-1.0 Lsize=  111247KiB time=00:09:30.48 bitrate=1597.5kbits/s speed= 377x    

In this specific case, the user didn't have permission to do transcoding, so enable that in Dashboard>Users>Allow video playback that requires transcoding.