@tonyabriscoe
Welcome to Connect, sorry your having that terrible side effect.

I sometimes have problems with Excessive belching from eating too fast, wrong food or laying down right after eating. I was diagnosed with SIBO, Small intestinal bacterial overgrowth. But that is an upper GI issue, yours sound more of lower GI problem. I treat SIBO with probiotics.

Found two articles that have recommendations, very similar:
Reduce gas after gastric bypass:
https://mdbariatrics.com/blog/essential-tips-for-reducing-gas-after-gastric-sleeve-surgery/
What's behind smelly farts after surgery?
https://www.perthsurgicalbariatrics.com.au/whats-behind-the-smelly-farts-after-bariatric-surgery/
It is shame the GI provider had no solution.
Have you thought of trying probiotics or seeing a dietitian about what types of food to avoid?