Thank you for the background and actions taken - good work I must say 👍
Though what is troublesome is this Notification in System Setting and then the Appearance issue which appeasers related
The only thing I see in my Appearance setting is as per below image.
There is nothing related to any Software Update which this notification is indicating
If I may offer a 7 step Trouble Shooting Scenario to work though, we might be able to sort this out.
It is suggested if going this route to start from # 1 and move down until either the issue stops or continue to last point.
1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.
2 - Safe Mode will also eliminate Third Party Software, extensions and drives from loadingÂ
3 - Does the issue present in this mode ?
4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.
5 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.
6 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.
7 - Download the Application Etrecheck directly from the Developer.
The application is free or paid from added features.Â
It will take a Snap Shot -Â both the hardware and software.
 The Report will Not Reveal Any Personal Information.Â
Post back the Full Report - copy and paste - >>>> using the Additional Text Icon ( 3rd Icon to last ) <<<<
We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.
