The workaround does make yay work again, though from liveusb I get
error fetching amdgpu-pro-installer: System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down
context: exit status 1
I can’t use yay -Syuu. (I did try upgrading yay the ‘proper’ way, but I kept hitting snags (from being in liveusb) and eight’s method was the quick and dirty way. I’ll do it properly and clean up that symlink after I get back into my desktop 
)
I’m starting to suspect that my issue might be separate, as this (seemingly) was a yay NVIDIA driver issue (and I’m using AMD in my case), and considering CTRL+ALT+F1/2/3/4/5/6 didn’t do anything from my blank screen.
I had the same issue. I could use TTY2 to log in and try to relaunch SDDM and then start X. On first boot, X would fail. On 2nd boot/attempt, I used the LTS kernel and everything worked normally. I updated my system again and rebooted to latest kernel. This time again I could not reach the desktop. Got an error “no space left on device”. Ran sudo pacman -Scc and then rebooted. Reached the desktop just fine and everything was up to date.
It was indeed a separate issue. Coincidence? I THINK NO- it probably was 
amdgpu.dpm=0 kernel boot parameter crashes on 6000 series GPUs. That was the source of it all. Though I ran into some interesting dracut issues pointing to a uuid (on root=uuid=xxxxx in the other boot parameters) that didn’t and never has existed.
You are using this one anyway? Proper package needed would maybe xf86-video-amdgpu ?
And indeed now w e have confusion with 3 different topics in one 
To have a hint about the one thing all 3 had in common?
Not reaching the graphical interface. What can be caused by a lot of different things