In the Filesystem section for that app in Flatseal, you need to add the path to your NAS drive (the same SMB path that it's mounted in the Files app). That will give your FF flatpak access to that location.
I use Proton Drive on Librewolf on Bluefin without issues, so that seems a little odd. It might be an issue with what access you've given the fkatpak. Flatseal is the right place to look.
I use Jetbrains, devcontainers, and distrobox on Bluefin-DX and it has been flawless out of the box. There's a single command to install the Jetbrains toolbox, which let's you then manage all their apps.
Couldn't recommend it enough, made my development lifecycle so easy.
It's just what I use, as I'm specifically looking for something which only notifies when things aren't able to report due to failure. Free for 20 checks which is more than enough for me.
If I were hosting it myself I wouldn't know if my own notification system had failed (since it wouldn't be able to report due to failure.)
The thing is that the privacy, speed, usability and configurability are so much better, it's only you that's missing out by making a statement like that. I'm sure it makes no difference to OP.
I switched in April and I cannot believe I was missing out on this for so long.
Or perhaps you'd like to positively contribute to the state of Linux gaming, and make some suggestions for the website in their post just for that: Requesting input: Bazzite’s website
Sure, I was just expanding on OP's Kinoite comment.
Aurora can however go weeks or months without a reboot (you don't HAVE to update), so that's still ok.