If you go to their release page, you will see two versions listed. The current stable release (13.0) and the explicitlly marked LTS version (11), both with clearly visible end of support dates. Not sure how much simpler it can get :)
Their project, their rules. I don't know why you would think that your ideologies automatically translate into something that's convenient or better for them.
Fair - I don't know why they've chosen the current numbering so I looked it up:
https://forgejo.org/docs/v11.0/user/versions/
They use SemVer so there really are Major breaking changes every 3 months by their own definition.
I suppose my assumption was that the software was basically "feature complete" but they must be working hard to add more to it.
https://codeberg.org/forgejo/-/packages/container/forgejo/ve...
At the very least, a stable "LTS" tag would help.
The significance of Forgejo 13.0 is basically zero. A two-year cadence Debian release is newsworthy. Even if this were an LTS this is still not that interesting (unless there is some other context or significance that I'm not aware of).
Rant over.