This question is usually asked a lot.

This started as a project to prove that you could check for updates without first pulling every new image to compare against, while that's not why it kept get getting traction my original answer to this question still seems true:

From Watchtower Docs - Arguments

Due to Docker API limitations the latest image will still be pulled from the registry.

And:

Do not pull new images. When this flag is specified, watchtower will not attempt to pull new images from the registry. Instead it will only monitor the local image cache for changes

It's also a different approach. With dockcheck you'd run it and then make the choice what you'll update there and then. Selectively choosing exactly what containers to update at the moment. Or have it completely unattended auto update a selection of images.

With the notifications, you can get notified and then have a sitdown and auto-update what you choose.

It's just different workflows and options.

The upcoming release will also add a new option to backup the image being updated and then autoprune old backups after N days. To allow for easy rollback if a new image breaks.

Watchtower hadn't been updated in like 3 years or something. It's a dead project.

Oh nice, yeah I havn't thought about suggesting a systemd-service thats neat! If you'd like you could contribute it as a discussion/suggestion/PR if you land on liking it, thatd be lovely.

With the image backups in the next release you could maybe even build some kind of auto rollback functionality.

Sadly no, only within the scope of the tag specified in the compose.

Renovate, WUD or Diun might be other options for that!

If you want automatic updates over major versions most images will have the :latest tag for that.