I'm lucky there is (at the moment) a weekly GJ jam nearby. I fully realize how tenuous and precious they are.
Prior to COVID I had been playing at Blugrass jams, but really only knew the basic campfire chords, and sang, er er croaked along to 3 chord songs. September 27, 2021, 6 weeks ago, I saw a Eastman DM-1 for sale on Craigslist, liked it and bought it. I learned a couple of each major, dominant and minor chords, with root on the low E and A strings. Knowing full well I play these few chords at half speed, I walked into my neighborhood GJ jam.
Tuned up, sat down, song started, and was immediately . . . well I couldn't remember any of the chords, looked at the guitar and wondered what is this thing - like I'd never seen a guitar before. Even worse, I had no clue where the group was in the song, no clue. I knew I was going to be overwhelmed, but I hadn't anticipated being paralysed.
This went on for 4-5 songs, I was tempted to sneak out and try this again in maybe 3-4 months.
I did not bolt, I decided to stay and to R-E-L-A-X. Just listen to the music, forget the guitar. So i just tapped my foot, counted beats and measures, follow the chord sheet and anticipate chord changes, and when song changed to Part A, B, etc. This 'active listening' went on for 4-5 more songs.
Then a song was called, and hey, I know a couple of those chords (without having to think them through) - so I will play those chords when they come up, and sit out the rest of the song. In short, this was my first jam . . . play the chords I know and when I can keep up; and sit the rest of the song out. By the end of the jam (about 2 hours), I was playing more and more of the chords, and was rarely lost in the song. Also, actively listening was a great way to appreciate chord progressions.
I think the jam was a success. BTW, all the other players were gracious (as I anticipated).