Volunteering with FIRST (I volunteer with FRC) can be a surprisingly fulfilling experience on its own! You still get the excitement of watching the competition, while getting the chance to mentor and support the brilliant young students making their way thru the program.
Many regions also have lots of regular returning volunteers, making the volunteer camaraderie even better than what I experienced while on a team.
You can look into combat robotics (smaller scale version of battlebots). I know of a few FTC alumni who have gone on to compete at different combat robotics leagues. The main league you can look into is the NHRL: https://www.nhrl.io/
There are different weight classes, so it is very accessible.
Many regions also have lots of regular returning volunteers, making the volunteer camaraderie even better than what I experienced while on a team.