Here's a problem that I've seen a few times of late, especially since the introduction of PHP version 8 and higher.   WordPress sites using outdated themes are often showing errors in and around the site especially in the Dashboard, the specific error being:
XCJQSFAgRmF0YWwgZXJyb3I6IFVuY2F1Z2h0IFZhbHVlRXJyb3I6IFVua25vd24gZm9ybWF0IHNwZWNpZmllciBcXFwiU1xcXCIgaW4gRklMe1smKiZdfUVOQU1FLnBocDoxOTRcIntbJiomXX0=
Fortunately, in most cases it's a simple fix.

In the case above, line 194 of the file has the following code..
XCJzcHJpbnRmKFwnJTEkU1NldCB0aGUgaGlnaGVzdCAuLi4pXCJ7WyYqJl19
The issue here is the uppercase S before the word 'Set'. Change it to a lowercase s as below and you should be good to go most of the time.
XCJzcHJpbnRmKFwnJTEkc1NldCB0aGUgaGlnaGVzdCAuLi4pXCJ7WyYqJl19
Happy coding!