I’d recommend you check whether you can restore a tagged file from backup and actually get the tags back. Only iCloud among the major cloud services maintains tags on iOS ( see Finder tags on iOS ) - Dropbox will transfer them from one Mac to another but not to other systems. Checking Backblaze now…
Update: the ZIP file from Backblaze when unzipped does not have the tags that were on the file I backed up. Interestingly zipping and unzipping on the Mac itself does preserve tags.
Another thing to test which I can’t do at the moment is whether external HD that are not formatted in AFS or HFS retain tags. I doubt it. If you haven’t been reformatting external drives before using for backup, they may be in NTFS or even FAT32 & hence not preserving tags.