I know this is about French fries and not potato chips/crisps how I'm thinking of them, but unironically tuna salad on toasted wheat bread piled high with crisps is my go-to comfort food when I'm down. I can only imagine French fries would have a similar vibe. I'd urge you to try IF you like tuna salad anyway.
Crisps / potato chips are also cold though, like tuna generally is, so they do work together. Tuna mayo with crisps works really well.
Chips / fries are hot though, so that heat will warm up the tuna, and lukewarm fish that should be cold is just wrong. Maybe if you had a small portion that you could eat quickly, but I can't see the appeal.
I could see that. Like, if you weren't getting specifically a tuna melt, then the heat from the chips could be off putting. I didn't consider that, I just thought "salty potatoes are great on tuna sandwiches"!