Hello @metasphere72, welcome to the forum!
The “Access is denied” errors indicate that Duplicati is trying to back up files that it doesn’t have access to.
My guess is you’re running it under your own user account and / or as the tray icon (not the service) so if you don’t have access to something, then neither with Duplicati.
If you don’t care about not backing up things that you / Duplicati don’t have access to then you don’t have to be worried. However if you DO want to back such things up then you’ll need to either give yourself access to them or run Duplicati under an account that does.
Yes - anything that Duplicati doesn’t have access to can’t be restored. However, it should be noted that Duplicati is not a “my hard disk died so I’m going to restore to a new one and boot back into the OS” tool - it is a “something deleted my tax and MP3 files so I need to restore them” tool. In other words, it does FILE level backups not DISK / SYSTEM level.
If you’re looking for a full system backup you might want to read through this thread where some other tools (such as Free Windows Backup Solution for PCs and Endpoints) have been mentioned:
How far is duplicati away from doing a "full" system drive image backup?