Hmm, that’s interesting. Maybe your single-user mode doesn’t have those kernel parameters added. Can you boot to your regular boot option and post the garuda-inxi from there?
Plymouth may be a red herring, but just in case you can test if removing the splash kernel parameter changes the issue with the shutdown hanging as in this thread:
Have you had a chance to change Plymouth versions to test? It’s been a while, but a few months back a version of Plymouth was causing issues and switching from the git to the “regular” version solved the problem, see this thread here:
Like I said though, Plymouth could be a red herring. If you remove the quiet splash from your kernel parameters (you can do this right in the Garuda Boot Options tool) you should see the actual journal output on the screen while shutting down–this could point to a clue, if you can make note of the process it is getting stuck on.
SDDM is notorious for holding up a shutdown, although in your case it sounds like it is freezing (as opposed to just taking a while). 