Yeah - I totally relate to the low-carb dining out experience being really challenging.
I have found two strategies to be really game-changing at the ordering stage (either to waiting staff, or directly to chefs in smaller places).
One is I just say, after finding out what has added sugar to what could be a great low- carb option, "I'm really sorry about this - I have diabetes. So I have way too much sugar in my blood already and I can't add any more to it without it affecting my lifespan!" No one argues with me, thank goodness.
My country is a high blood glucose dysregulation country - estimated at a third of all people, so most people understand a bit about it, and many cafe owners now in the biggest city, Auckland, are Asian or Middle Eastern, and definitely Indian - all places with high levels of type two nowadays, or at least - prediabetes. I am finding, nine years post diagnosis, that many cafe and restaurant staff have some form of blood glucose dysregulation themselves now, or a close relative who does, which matches the stats. So - much greater understanding.
The second one I do if I am feeling in the mood - I apologise for elaborate ordering by saying I am mildly OCD, (Rightly or Wrongly.) and make all the condiments on the side. Everyone knows about OCD, and the wonderful Sally character in the classic 'When Harry Met Sally' movie did a wonderful thing in normalising putting everything (for us - potentially dodgey with hidden added sugar) - on the side. This strategy has gone a very long way I must say. As a mental disorder - folks are very kind and understanding, and it has been a fantastic shorthand.
So when I sit there tasting the condiments on the side for sugar (which there invariably is), and leave it - no one says a thing and treats me kindly.
What I have had less success with is with my 'deconstructing' my order, in order to reduce/eliminate the sugar and carbs. I've had some awful experiences where I have been told off by cooks and waiting staff for leaving the fries, and taking the buns off burgers and leaving them on the plate. (Which is where, from one cook, I got the word'deconstructing' my food from. I never went back to that cafe, of course.) As I paid the full price I found this quite dreadful, and disturbing, which is one of the reasons I always explain with the T2D, and depending on how jolly I feel - the OCD.