They have a forum but now discuss the switch to GitHub Discussions[1]. The issue about oxidizing everything is here[2]. If you want to help the project there is a number of issues[3] that can be done, in particular syncronization with the Tectonic mainline and XeTeX code update[4]
[1] https://github.com/tectonic-typesetting/tectonic/issues/766
[2] https://github.com/tectonic-typesetting/tectonic/issues/459