Hi,
I’m having this issue too. Previously I couldn’t even upgrade using nixos-rebuild switch because it would just quit the DE during upgrade. Rebooting/Shuting down would also hang.
I tried sudo bootctl install and it partially solved the issue - rebooting/booting/shuting down no longer hangs and I’m able to log in. But I still cannot upgrade the system at all. Every time I do nixos-rebuild switch it would just give me could not find any previously installed systemd-boot and exit. Does anyone have any idea how to fix this? Thanks so much!