Solved. So I had the same problem, screen freezing, sometimes curser moves, happens after a few minutes, I couldn’t install most recent update, I tried freeing up disk space, starting up on Safe Mode, aimlessly looked at the Log Files, then I found somewhere on this site where they suggested the following steps:
System Preferences->Icloud->Manage->Icloud Photos—>Disable and Delete
I restarted computer, solved. Dowloaded the most recent update. Now I am going to Undo the Icloud Photo “Disable and Delete” to see if I can replicate and solve the problem again.
I will report back.
If this works for anyone please reply amd let us know.