So do others thoroughly check out the menu before going to a new restaurant

[IHopeYouStepOnALegPiece]

Or are you like my insane friend who will look at the menu tomorrow when we go for brunch and decide in the moment

Also, how many mains is too many for brunch because I can’t decide between 3 full meals off the menu

I like to know what the restaurant serves before booking. I don't see the point in booking to go somewhere if I likely won't like the food.

Good small independent restaurants often have a very limited menu - perhaps just three choices of each course - so I always check in advance that there will be something I like.
DD is veggie, so if she is coming we pick a cuisine like Indian, with lots of veggie options and check ahead too. Otherwise she gets stuck with yet another bloody beetroot tart or mushroom risotto!

I always check because of allergies and vegetarianism. However good the restaurant if they only have one veggie option, or put bloody shellfish even in their meat dishes, we can't go.

I always check that there will be more than one vegan option. It is easier now, mainstream restaurants in the 70s and 80s were often no go areas for vegans.