[senectus1]

the r/FODMAPS sub is pretty active.

The main issue I see though is that if you're going to include processed foods, things will get complicated.

The names for various ingredients change in some countries ie: Sorbitol is also known as glucitol, D-Sorbitol, Sorbogem and Sorbo .

I use this example because Sorbitol is a sugar alcohol that affect FODMAP types.

You might do well having a chat with the Monash University, they have done a lot of work on this and have even published an app for people to check and see what sensitivities particular foods might have.

https://www.monashfodmap.com/

That database might be crucial for your site.