On the archive:

For versions <= 1.1.1, the archive is stored in a sqlite database. This has the advantage of being independent of the tracker, but also leads to problems when you decide that you want to change the location used for storing downloaded videos. Also, the database can become corrupted (there are a large number of read/write operations due to all config settings also being stored in the same database).

For versions >= 1.2.0, the archive uses QtGallery. This has the advantage of allowing to change the location whenever you like, without any risk of messing up a database and losing a record of downloaded videos. The disadvantage is that the archive folder must not be hidden from the tracker, else you won't see the videos. If you want to view videos from the 'old' archive, simply change the archive folder to the 'old' one (providing it is not hidden from the tracker. You could rename it if necessary), or move the 'old' videos to the current archive folder.

The other change is that thumbnails are now stored locally in a hidden subdirectory named .thumbnails.

The widget no longer provides access to archive because the purpose of the widget is to provide an 'at-a-glance' view of the latest videos, whether they be from your subscriptions or whatever.