This happened to me I think in 19.3. If you run it in terminal it usually tells you what failed and you can troubleshoot from there. Sudo can sometimes get it to run. Try that, maybe it will help you out.

No. There is a system tray icon on the bottom right of your desktop that looks like a shopping bag with an exclamation point inside of it. Click that and it should walk you through the update.

Alternatively, look for the program called System Reports in your programs. You should make a backup of your system, as sometimes things don't always work smoothly and you might lose things. Small chance of that happening, but still a chance.

I use Timeshift to make backups.

Hope this helps.