Comment 3 for bug 1847596

Can you attach the content of your /boot/firmware/config.txt?

I suspect it's lacking the vc4-fkms-v3d overlay which is now required as of the pi4-compatible kernel (I'd originally, mistakenly, thought this was only required on the pi4 but it turns out all pi models need it). Tomorrow's dailies should have this change, and if you update to the latest u-boot-rpi package it *should* migrate your boot configuration to include this but otherwise you may need to manually add it in.