Ah. I don’t know if this helps, but you can see all the communities for a given server and search. It’s hard to know what to search for sometimes, but for the most part it should have relevant keywords. I think you can also search All which will sow results from all fediverse instances.
From what I understand in how federation works, you shouldn’t need to join any other communities as they will all show up here. If you go to the All tab (rather than local or subscribed) you should see a ton of other stuff coming in. Then you should be able to subscribe, block or just ignore things. Once you have subscribed to quite a few communities then the subscribed becomes more useful to keep up on the things you are really interested in.
I didn’t see a paywall when I clicked on the link, but you can try this:
https://12ft.io/proxy?q=https%3A%2F%2Fwww.popularmechanics.com%2Fmilitary%2Fresearch%2Fa43713837%2Fdarpa-power-military-outposts-wireless-laser-energy%2F