I've posted before about my eating experience after bariatric surgery, but to sum it up:
-- If you haven't explored the instructions given to bariatric surgery patients for how to eat for the first several months after surgery, you might want to do that just to see if there are any tips you might find useful. A lot of work has gone into building this guidance over the years, so you might as well benefit from those studies.
-- If you can't eat a balanced diet, it isn't the end of the world. Prioritize protein (make your own protein shakes if necessary, which gives you total control, and consider tossing in whole frozen fruit or green vegetables if you can handle them). Consider the key supplements: iron, calcium+D, multivitamin, B12, and B1. (Don't take iron and calcium at the same time, since they fight each other.) Ask your PCP to order blood tests for all of those several months after the surgery, and make sure you keep asking for updates to guide your supplement choices over time.
-- There were many foods that triggered nausea for me during the first year or so, but most of them have become gradually less problematic. If you find you can't eat something, try again with a small amount in six months, a year, etc.
-- Consider going through a FODMAP exclusion diet if you are really having difficulty pinning it down. Importantly, it doesn't actually have to be a FODMAP problem (turned out that it wasn't for me) for the diet to be helpful, because it gives you a systematic way to identify challenging foods. The FODMAP exclusion diet is not for everyone, though, since it's very disciplined and takes a long time to get through.
-- I lost the ability to handle garlic, but shallots are fine and make a reasonable substitute. That problem appears to be permanent, but my ability to handle chilis seems to be returning, although it's taken about a decade. It really helps to explain to the wait staff in restaurants that the issue is NOT an allergy and is just a strong preference, because kitchen staff these days are trained to panic about allergies and my issues won't actually kill me, which is very different.
-- Insurance reimbursement rates for dieticians are so low that it's hard to find them. If you do, make sure that they have experience with patients who have had your specific procedure or are have dealt with your specific symptoms.
-- You may find that smaller meals are better, which means multiple snacks instead of full meals. I now manage meal sizes by when I start sneezing; apparently it's a vagus nerve thing, and I know that if I try to push past it, I'm guaranteed to head to nausea and potentially vomiting. I'm not saying sneezing will happen to you (pretty sure it happens to almost nobody), but you can absolutely watch for the earliest signs that enough is turning into too much, and just rigorously stop there.
-- Don't let yourself get dehydrated, which will make it all worse. Track whether you are better off drinking with meals or between meals, since this might impact your symptoms.

Hope something here helps!