I have made a step-by-step guide so you dumb fucks can follow.
click on your username in the top right corner
Go to “Settings” and then switch to the “Blocks” tab
Type in the name of the community you want to block
Save your changes. That’s it! See it wasn’t so hard.
New communities pop up, and older ones that didn’t have many posts sometimes get revived. So if I have the time and inclination I look at All after my Subscribed.