I'll reply and be polite as I can be whilst still following the 'Personal / flaming attacks are unacceptable' type rule as on https://docs.moodle.org/dev/Moderator_guidelines (currently in maintenance so I can't post the specific link), and so state things from my understanding / point of view as a matter of information and not as an attack, personal or otherwise, on the other version.
I am aware of the version and have reached out / contacted the developer on many occasions with a view to collaborating. Eventually I did get a reply, however to state what happened to get to that point and the nature of the reply would be a violation of the forum rules. So, the outcome of this is that I very much doubt there will be collaboration to stop the confusion that is clearly going to happen. All I can say is that I have been given developer rights to continue to develop and maintain Adaptable on moodle dot org and GitLab (https://gitlab.com/jezhops/moodle-theme_adaptable) by the original owners.
I have downloaded and installed their version, and as far as I can tell, its the codebase as of 1.5 - 2 years ago or so. Thus probably does not contain the fixes / improvements I've made since then, but does contain functionality that I wrote before then.
Testing wise, I looked at one of the things that have changed between M3.10 and M3.11 being the 'blocks' method, this has been made to work, however the '$fakeblocksonly' addition is not parsed down to the parent version of the method and so the parent theme (Boost) embedded layout won't work as core Moodle intends. I've also seen other issues, but clearly and I hope you'll understand that I wouldn't want to spend my time reporting them.
Clearly all my changes since the 'fork' are public and GPLv3 licensed and they could legitimately copy and integrate them if they so desired.
If any of my words are a violation of any rule, then I'll immediately retract them by editing my reply. I really hope this helps to go someway in answering your question.