macos 10.15.5 won't update

If you are running 10.15.5, then there are no updates. That is the latest version. If you are trying to update TO 10.15.5, then Download and Install the macOS Catalina 10.15.5 Combo Update.

I've been trying to update to 10.15.5 for a few weeks now. The pop-up to install appears, I hit "install now" and it requires me to reboot. I restart, and nothing. I've done then a handful of times over the last few weeks. Yes I've tried updating while connected to power.