Sync for Lemmy

I agree, it should be global by default and changeable per account

That's definitely how it worked on reddit. He's using the original reddit app as the base. Cut him some slack right now, he's still working on the lemmy specific features. Stuff like this is perfectly functional, so tweaking it is most likely a pretty low priority.

i think you can export the settings from one profile and import them into the other

I'm pretty sure my app's font size and media handling didn't change every time when I switched accounts in Sync for Reddit.

It changed for me too on the reddit app, as it does on the lemmy app. Best thing to do I export settings and import into other accounts

I agree. This is one thing that is too much akin to how things work on Reddit.

On Lemmy having 10+ accounts is not really exceptional and backuping/restoring each time you change one settings is not sustainable

I like the OSMand approach: whenever you change something you get an extra prompt on the bottom of the screen whether you would like to make the change in all other profiles (driving, browsing, walking, public transport, cycling etc) or keep it only here or revert, as pictured below: