I don’t know about automatically but I have it on my actions. The three little dots in the top right you can bring up the menu and if hide read isn’t there you can hit the three dots again on that menu - action visibility, to add it. Can hold and drag the order of the actions too.
I’m very new too but my understanding is that each instance can have it’s own specific content. But, you can see all content from any instance if you sort by “all.” If you sort by “local” then you will only get posts from the instance that you’re logged in to. If you go to subscribed then you’ll just get stuff you’ve subscribed to in that instance. Could be wrong tho lol
Shokz is a brand that makes them. I haven’t had a pair but a student of mine had them and liked them.