No updates since a long time

Solution 1:

Lots of people ask this question between mid-December and the first week of January when a lot of the development team steps away from the keyboard to enjoy some time doing other things, like spend time with family. Updates generally resume around the 10th of January most years so long as there are not major security vulnerabilities discovered over the holidays. If you haven't seen anything by January 15th, then it's time to investigate.

Solution 2:

Updates get published at various sites, so why not monitor such a site.

I work with the Ubuntu Weekly Newsletter, the last issue UWN #633 has a very clear

Security Updates

No activity this period.

A single mutter update was listed for that week for focal/20.04, but if you don't have mutter installed you won't have had that updated package.

There were many more the week before (UWN #622), but you can check yourself (it's a weekly publication, and you know your release)

The latest release usually has the most updates (that's groovy/20.10, of course ignoring development/hirsute). Older stable releases get fewer generally (only back-ported security updates)

If it worries you, you can always scan the Ubuntu Weekly Newsletter at the Ubuntu Fridge / UbuntuForums / wiki & other places where it's posted.

In the end, we all need to check it ourselves, as we tend to change the packages we have installed (you will also know your release, as you didn't say - I don't know it, so used focal as example as it was the release of another question).

I'm using Ubuntu Weekly Newsletter as example of a place you can check, selecting it because it's one I'm very aware of being involved with it since 2015, but it's not the only source for such information.