My computer is not compatible, what is going to happen with apps updates?

Eventually you might need to replace your computer but not for a while. You would be best served by devising an upgrade plan to acquire a new Mac when the time is right for you. I also have a Mac which can't be upgraded beyond Monterey and, expecting this, a year ago started to save towards my next iMac.

The applications you have on your Monterey system will also serve you for some years to come, but one by one the applications will require a newer operating system. However, it's worth noting that I have an old MacBook Pro with High Sierra 10.13 and it is a useful notebook when I'm away from base and need a Mac to use. It's a long way short of my primary Mac, but still capable of many tasks despite having an OS which is now five years out of date. Many of the applications though are still the current version. Quite a few developers have their system requirements some distance in the past.

In the past Apple has been known to issue the occasional security updates for the previous version of macOS but these should not be expected regularly or at all.