i did update my machine with pacman -Syu. after rebooting, i cannot login. i con see this error Failed to start Virtual Console Setup a tiny second right before log in screen. i had to capture it in slow mo to able to read it. i attach the image below.
and on the login, after i enter my username and hit enter it just hangs for a while without asking the password and asks for username again. it acts like when you enter wrong password.
Fix
turns out /bin some how got messed up. thanks to @wwwgem, i looked into system logs (journalctl) and fixed it
Today, my nixos took 50gb of drive space to update itself. I allocated 60gb for my root partition and nixos itself takes 20 already. Nixos is hot garbage in that regard. Nixos is stable but bloaty, arch is sleek but wonky.