I've created a trs80gp Facebook group and a trs80gp Discord server as venues for more interactive discussion. You may not find many people there but I will keep an eye on them myself.
The most active TRS-80 forum is the Tandy Radio Shack section of the Vintage Computing Federation forums. There is also a somewhat less busy Tandy Computers forum on AtariAge and a very lightly used TRS-80 subreddit. There are also a handful of facebook groups dedicated to the TRS-80 models that trs80gp emulates.