You need to edit the /boot/firmware/cmdline.txt.
If you want 1920×1080 output on HDMI-1 add
video=HDMI-A-1:1920x1080M@60
to that file. Example:
root@rpi4b@~# cat /boot/firmware/cmdline.txt video=HDMI-A-1:1920x1080M@60 console=serial0,115200 console=tty1 root=PARTUUID=9254db70-02 rootfstype=ext4 fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles cfg80211.ieee80211_regdom=US
It should be on one line with NO newlines.
Reboot the pi.