Unable to restore Time Machine backup to a different computer

I have a MacBook Pro 2017 that was sent for replacement. The system was always synced with Time Machine. I have a temporary MacBook Pro 2017 I am trying to restore to, but I can't get it to work. The Time Machine backup is on a NAS partition (Synology DS216). The path from the NAS' perspective is: > smb://SynologyDS216/volume1/TimeMachine The path from Finder's perspective is: > smb://SynologyDS216._smb._tcp.local/TimeMachine I reboot the computer to macOS Recovery, it finds the NAS, I can connect to the partition providing the username / password, and then nothing happens from there. It stays on the same screen. It is the same behavior whether I try to use the auto detected path, the NAS' path, or the path Finder creates. No backup appears. When I connected with the original Mac, through Time Machine, I can see the files, the history, etc. so the files are there. Now I have two questions: - Is there such a thing as a 'machine backup' vs. 'just some folders backup'? I had a lot of folders exclusion in my Time Machine settings, so maybe the files are there but not the OS. - If I connect to this backup through Time Machine, instead of the system restore/migration, is there a way to connect as read-only so the temporary computer will not start to edit the backup? As a side note, the backup is from macOS Catalina (on a MacBook Pro 2017 15") and the temp laptop is running macOS High Sierra (on a MacBook Pro 2017 13"), if that makes a difference.