Apps Constantly crahsing and macOS randomly rebooting. Overall state of macOS software unstable.

I knew that you had reinstalled the OS but was unclear as to whether you actually erased and reformatted the hard drive. Since you clearly have done so, that tells me that you either have a physical equipment issue or some other software is the culprit as I noted earlier.

Maybe someone else will see something I have missed. You have certainly done a lot of the right things. I suspect that some bit of software is the culprit. I would (1) Restart in the Safe Mode if you haven't done. so. That clears a lot of problems. Be patient as it can take up to ten minutes while the OS is doing repairs and cleaning its caches. (2) If that doesn't worket rid of any apps you don't need. (2) Then try deleting and reinstalling as many apps as possible. The final thing would be to save your files to an external disk, then reformat the HD, which erases everything, then reinstall Os & apps and copy files back. Hope some of that works.

I agree that it seems to a hardware problem.

You could try running Diagnostics, and seeing if it tells you anything.

Start your mac and immediately press and hold the D key.

Let us know.

It may be necessary to take your mac to be looked at, at an Apple store or authorized repair facility.