I have the same problem with a acer 28inch 4k monitor in 4k mode on rock pi 4b+ v1.73 running on nvme .The right part is also gone with a sort of overlay in fullHD mode its okay
on armbian version 23.02.2 with kernell 5.15.93 no broblem the problem is with Armbian 25.5.1 with kernell 6.1.30