One issue with alternative smaller platforms can also be them becoming cesspools of users banned from the big platform. The first couple of Reddit alternatives quickly collected the racists and jailbait porn.
A viable alternative platform needs more than extremist niches.
For a small project I recently switched to fossil from git. It’s also distributed version control, but includes a bug tracker, wiki, and other stuff as well. It’s minimalist, but hosting yourself is super easy.
Default git over ssh is often enough as well. Combine with any bug tracker and CI you like. You don’t need to use an all in one tool like GitHub.