Just curious: what feed are you using? Local or All? I use “Subscription” (I use the Italian UI so I’m not 100% sure about the English naming) and I just see the communities I subscribed to

you are the one talking about the left mouse button … BTW on almost any OS you should be able to config the behaviour of the click (on KDE I have letft+right click to emulate the middle click)

you can just middle click to open in a new tab