Seen a lot of different opinion in this, but personnaly I would recommended this.
SimpleX, for the most privacy (but not really appropriate here)
Wouldn't use any of threema wire and else, as it's not the best.
A good option in the case of this project is a matrix server, if the group is public it's the best thing. Try to host it somewhere else than matrix.org.
Will have no real hiding but surely anonymously if done correctly
Seen a lot of different opinion in this, but personnaly I would recommended this.
SimpleX, for the most privacy (but not really appropriate here) Wouldn't use any of threema wire and else, as it's not the best.
A good option in the case of this project is a matrix server, if the group is public it's the best thing. Try to host it somewhere else than matrix.org. Will have no real hiding but surely anonymously if done correctly