I just did a full system update today, first update since 2021.08.18 and KDE updated with it. Now, my system tray is missing from my panel, multiple icons have been removed from my task manager on the panel, and several widgets on my desktop are removed. I tried adding my widgets back to my desktop and panel, but they won't stay or get added at all. I'm about to downgrade and hold back updates because I need to be able to see my system tray. If there is a solution or workaround, I'm open to try it, but I'd rather not have to reinstall and set everything up again.

Distro?
Have you checked that there aren't more updates to install?

cypheroxide wrote: If there is a solution or workaround, I'm open to try it, but I'd rather not have to reinstall and set everything up again.

The best workaround about linux systems is to create a new user so all previous user related settings will be resetted.
So just create a new user and login with it and give a try. ( dont forget to add that user into related groups (/etc/group file) just like your previous user
i mean if your previous user was cypher and new user is oxide then add oxide into same groups like cypher have .
for example if the line was like this :
docker:x:963:usta
change it to
docker:x:963:usta,oxide(yournewuser) ( add coma then add new user name )
and reboot your system and login with your new user