To be honest, I have zero expectation that a restaurant or eatery will have any interest in any dietary requirements, unless they think they will be sued. Their offering is their offering, and in the age old way,........ "buyer beware."
From any given menu I just choose the least, worst/best option and pick what I can to eat from it. Sometimes that'll mean I leave stuff on the plate, or ask for a side plat to put something onto, but that's up to me.
As others have said, I'll try to navigate a menu before going. Getting along for 10 years in, folks just accept how I eat, but at the outset if someone asked why I wasn't eating x, y or z, my response was I'd had some routine blood tests that showed a few things in my diet weren't doing me any favours, I was was giving them up until further notice. Only once was I challenged on that, by the wife of a retired GP, who obviously felt it was her job to know the detail. I just explaine she didn't have enough life left to hear the story, laughed and moved on.
My condition is my condition to manage. These days I do have to be gluten free, and when choosing in a restaurant will always confirm I am having the gluten-free option.
Its tough going at the outset, I know, but trust me, it gets easier.