Sorry, meant to reply sooner.

I don't know what your environment looks like, and I wouldn't try to fix it anyway—that's out of scope for a lemmy comment. I do want to mention some info that might be interesting/relevant for people reading this thread:

• The GTK file chooser, if that's what you're using, already has better file previews.
• Sadly, programs won't always use the best method available to do things. While Upscaler gives me nice image previews in the file picker, my installation of Firefox hasn't even updated it to GTK 4.
• Portals seem to be a good step towards more uniform and predictable user experiences.
  • "[...] any application can use portals to provide uniform access to features independent of desktops and toolkits."
• Point being, better things exist and are on their way. Adoption is slow, but we're getting there.
• ...And on a semi-related note, if you have previews for certain file types, but not for others, check if you're missing a package. That took one search and one command to fix something that'd been bothering me for weeks.

Exact issues and how bad they are depend heavily on your setup, such as which desktop environment you use and which software (& versions) you have installed. That seems to be a common description of ~~UX~~ problems in the Linux ecosystem, I wonder why :^)))

But hopefully I managed to spread some positivity(?) about the state of things and where we're going.