You are clearly wrong as Ubuntu disabling x32 apps here is what caused the problem. If a distro as big as Ubuntu could never be trusted to test Steam, what chance does your distro X have?

I do not trust people uploading Flatpaks for distribution to cover those things (even, or perhaps especially, if it’s software they’ve developed—the number of blind spots developers can have about their own environments is terrifying).

All this flies out of the window when it's your distro that's introducing the bugs as was the case here.

“Why does [preference X] not work inside this Flatpak?” is not an uncommon topic.

This is legit and I have to give you this. It's not perfect but to me, can't ever recall a time a workaround was not available. Most of the time, you'll find an issue like a plugin that is hardcoded to call to a library using the standard distro path or something like that.

But more users catch this stuff and share solutions to the Flatpak community.