Check your flatpak permissions for starters.

Flatpak apps operate more like containers and not a full blown sandbox, unless that has changed recently.

This is an interesting blog post on the subject: https://hanako.codeberg.page/

Also, try flatpak run org.mozilla.firefox to see if you can launch a browser manually.

Disclaimer: It’s been a bit since I have used flatpak, so take that into account. However, I do work in security by trade, so my quick notes may point you in a decent direction at a minimum.