I would never upgrade without doing a backup of my system so I could revert back. I assume you did not do this?

Under Arch it hasn’t dropped to Stable yet, so unless you are running the testing branch, you won’t have to worry. I think it took 5.27 two weeks or so to get to the stable branch after its “release,” so you are probably looking at early to mid March. By then, we should also have Plasma 6.1 drop, ie, updates.