Go back and look at all the good faith replies to you, and notice that you haven't replied in kind. You seem like you have a strong and incorrect agenda to push, without being willing to take on any new information which people are providing to you.
You only harm yourself by being fixed in your mindset. There is a very strong correlation between success and people who are able to take on information and grow.
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.)
I would consider docker very easy to use and well worth exploring. The benefit of Docker is that it runs exactly the same on any system, no matter what the underlying OS is.
Here's how difficult it was to set up Immich:
Download a docker-compose.yml file, which describes the options for the Immich server.
Put Aurora on it - an improved version of Kinoite.
https://getaurora.dev/