I had similar issues, and tried the same to no avail. The only thing that worked was a complete reinstall of the operating system. Am guessing you might need to do the same.
fwiw, I was of the same opinion and update cadence, but then just installed Big Sur (from Mojave) and it's been totally fine. The only exception is that Omnifocus 2 bugs out a bit and shows a graphical artifact that they refuse to patch.
I agree, although in fairness they've come out with a v3 that's fully supported. Since it's only marginally different, and aesthetically less appealing, I haven't bothered buying it.
Thankfully it was something else, and I was able to keep catalina.
I refuse to be a QA engineer for apple for no pay. Running one OS version behind has worked really well so far.