brambler Hi there! Welcome to GrapheneOS and the community!
Currently, Vanadium is updated as part of OS updates instead of as a standalone app like Camera, PDF Viewer etc.
This is for multiple technical reasons that I can't recall now (sorry!). I do know that one reason is that up until very recently, Vanadium did not have its own app ID, which was one blocker, but there are others.
On releases, and the release channels:
Releases are tested by the developers and are then pushed out via the Alpha channel. The release is then pushed out via the Beta channel shortly afterwards. Finally, the release is then pushed out via the Stable channel after being tested by some users using the Beta channel. In some cases, problems are caught during Beta channel testing and a new release is made via the Beta channel to replace the aborted one. In general, it's not possible to downgrade unless a downgrade update package is generated, so use the Stable channel if you cannot tolerate dealing with temporary issues while a new release for the Beta channel is being created.
We're always looking for more beta testers, and there is an alpha/beta testing channel on Matrix! The more people testing with diverse devices, apps, habits, the faster we can ensure the release is good to go and it can be pushed to the next channel with more certainty. If that's something you'd eventually feel comfortable doing, feel free!