I cut out ultra processed foods: gradually. 3-4 years ago I realised that the mid-morning bun/scone/eclair XX fill in the gap was causing bloating so badly that I was unable to eat for 6-8 hours. This didn't happen in the day, unless we were out and about.
Gradually we increased more veg to my diet, cutting out all UPF. Until New Year's Eve 2023/4 - I had been eating stodgy over C.mas which impacted, I thought that I was going to die. Back to no biscuits, cakes, scones and gut improved.
In November we went away where it was toast and butter for breakfast, not my usual muesli with milk: again I began to feel better - no afternoon bloating. So it's been toast with butter since for b.fast. Sugars cause my irritating continual clearing of throat, i.e. Coke, chocolate

, peanut butter. This has been difficult in recent weeks but I am slowly getting there.
I blame age

though in my head I'm 17.

. I think it's going to be a continual food adjustment for a few years B4 my gut settles, whether my slow transit will improve remains to be seen [not literally

].
Lunch time is my most difficult meal to make choices for.
Let us know how you get on with the investigations and whether taking note of your total intake: fluids and food: for 5-7 days/nights, would show if U need to cut out anything.