This forum is a good place, since most of the people responding to posts here have significant experience in using LAMMPS and discussing with users about LAMMPS. I sometimes post a message asking for feedback or when new test versions are available. You could respond to that. The last one is here:
If you would rather start a new thread, you can do that too. Just put it in the “LAMMPS Development” category.
This forum is the best choice, if you have some general suggestions and would like input from other LAMMPS or LAMMPS-GUI users.
If you have specific issues, i.e. a bug report or more technical requests, then it would be better to post those on GitHub as a “Bug Report” or “Feature Request” issue.