A "Tankie" is someone who approves of authoritarian communist regimes. This is a reference to the use of tanks by such regimes against anti-communist protests. They had a powerful presence on lemmy before any reddit migrations occurred.

In terms of some communities that seem decent...

mander.xyz has some really decent science communities and generally they don't head off into politics land.

slrpnk.net has some decent communities regarding green energy and the like. They naturally have some more political posts, but it isn't too insufferable.

I've been pretty happy with the posts I see from lemmy.sdf.org, still computer stuff but they seem pretty decent.

@realcaseyrollins@narwhal.city has a good habit of posting a lot of either neutral or non-political content over on narwhal.city in various communities. I think he's also over on kbin.projectsegfau.lt, but I don't know too much about that server.

cyberpunk@lemmy.villa-straylight.social has been reasonably decent with lots of cyberpunk stuff

It seems like a lot of communities dropped off a cliff about a week ago.