What OP didn't share, btw
So basically, they deactivated native 4k on the PS5 back compat version, none of them are current gen versions. Congrats!
I don't think you can have a magical resolution option for PS5 only in BC. So it is more like they couldn't run on PS4 Pro at 4K (even dynamic) bc of technical or performance issues, therefore no 4K on PS5 right now until native.