I’m using Simon Tatham’s Puzzles for nonograms.
It’s basically this webpage in app form: https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/pattern.html
It doesn’t result in a pixel art picture when you solve it, if you care for that, but the solutions do have contiguous regions.
Well, if you’re self-hosting GitLab, there might not be much of a difference. Codeberg is hosted by a non-profit organization, so you don’t have to self-host it.
The open-source software that it uses, Forgejo, is also more so developed by the community, rather than just one corporation, who could change the license for future updates at any point.