Replying to both parent comments here:
I do a fair bit of promotion on YouTube[1] which has resulted in a vibrant community around the software, and I am now creating an official, free GUI[2].
In this specific case even if there had been a trademark in place, the person in question had not used the name of the project at all, but had decided to aggressively market it in community spaces.
Ultimately after much reflection and experiencing first hand how easy it is for people to abuse (in my opinion) the option of deliberately hard-forking and introducing breaking changes to funnel people towards a paid piece of software (in this case, a GUI) that will _only_ work with their hard-fork, I concluded that preventing this kind of ecosystem fragmentation is more important to me than an "OSI-approved" badge.
[1]: https://www.youtube.com/@LGUG2Z
[2]: https://www.youtube.com/watch?v=zZKjBMt4kZ4