Hi there, welcome!
You should start from here.
My best guess would be to use a live USB, chroot, and enter update, which is more complete than the sudo pacman -Syu.
But it could be a lot of things. E.g. Nvidia drivers?
When you are in chroot you could provide also your inxi -Faz and maybe check the list of packages upgraded in the last update which made troubles…
Edit:
Another thing you could try, since you probably just upgraded to kernel 5.15.2-zen1, which is very new so can have some regression issues at first, could be to install, after chrooting, the lts kernel
sudo pacman -S linux-lts linux-lts-headers
After that, you’ll find it in the grub under advanced options submenu.