Forcing rescan of a watch folder looks for new files, removed files, and files with different modification timestamps, and then reports those differences to Roon’s database.
That’s it. If files haven’t been removed, added, or had their modification timestamps changed, Roon will not notice. It would be prohibitively expensive to do anything more than that at the folder level (keep in mind: when Roon is started it does this scanning operation on each folder. It has to be cheap enough that we can actually do it without user prompting without causing disruption).
If you want to force Roon to re-extract tags from the whole universe, Select all in the album browser and select “Re-scan Albums”. That should do exactly what you are looking for. It will re-read the tags regardless of the modtimes. And it might take hours to do it, because that’s a lot more work than checking timestamps.