I'm probably not the best person to answer because I blocked !memes@lemmy.ml but it seems like the latest trend is to post old school memes. It gives the older users a sense of nostalgia to a time in the early days if the internet. So I suspect a lot of people have focused on !antiquememesroadshow@lemmy.world since it's now a community.
Just like any internet trend, it will come and go quickly until the next fun and exciting thing takes its place.
Meta unfortunately decided to call their platform a very basic name, the same name as a core feature of Kbin and Lemmy.
PixelFed, Friendica, Peertube, and Mastodon (all part of the fediverse) don't really use comment threads (Mastodon sort of does) but for Kbin and Lemmy it's basically the most unique part of it, other than being a filter for various links to other pages. So they are often refered to the part of the fediverse that uses comment threads.
Kbin and Lemmy have been referred to as the threadiverse for much longer than Meta's Threads has been around, even before it was known only as Project 92.
You can also "install" the mobile web version as an app. Just go to your home instance lemmy.one and and fromthe menu on your phone's browser, there's usually an install button.
Probably the best way to contribute buildings is using the JOSM editor and the buildings plug-in.
It's only available on the computer and it has quite the learning curve, but it's a very powerful tool for serious editing. Usually the iD editor is good enough for easier editing than on mobile.
I think that may happen when those communities haven't federated on your instance. You should be able to copy the link and search for it on your instance, it usually takes several seconds for it to appear because it needs to resolve the link to the community.
Once someone is subscribed to that community in your instance, those links should work as expected. At least, that's my understanding of it.
hallelujah?