Thanks again! Here is my Feb 2022 news:
I updated CB to 2.7.1 and then tried the latest version of CJ forum. No errors yet (still using their older library). So... then tested again using the CJforum latest library. Everything in their extension worked - listings , replies, small features - etc etc... UNTIL I tried a new forum post. Then I got 500 error again. They are using Guzzle 6.5, the last I heard. Waiting to see what they have to say about my latest development. I really like their forum, it has all the features we need...