There are some good Irish players sessioning in Houston. Inquire at McGonigal's Mucky Duck, The Penny Whistle, The Chelsea Wine Bar and The Brew:30 Tap House to see what's currently going on. If you can get in touch with Diel Moran (fiddle) and/or Larry Mallet (flute) you would get a good grasp on the lay of the land, so to speak.
The Bay Area Bluegrass Association (nearby in League City) has a large monthly jam and performance.
Hickory Hollow (near West University / 610) has a great weekly bluegrass jam that temporarily suspended because of Covid - I don’t know if it restarted but it is a ton of fun and I can’t wait until it resumes.
The Houston Folklore Society (you can find it on Google) has various house parties, concerts, and jams and it has more of an oldtime focus.
There is a thriving Celtic scene in Houston (in part because of a private school that has the best bagpipe band in North America) but I am not sure how to plug in with it.
I am in the Houston area and can play and sing a fair number of Cajun songs. Moi, je suis pas cadien, mais je connais un ‘tit brin de la musique que ça joue dans la Louisiane. I wish there were a Cajun music jam in the area but I haven’t found one. But this website has info on a monthly dance at a veteran’s hall in the Houston area: cajunfrenchmusic.org/houston/
If you are ever in the Austin area, try visiting the Austin Friends of Traditional Music.