I can speak to Jerboa and on desktop. On Jerboa the block is in the 3 dots menu, in the upper right, on desktop it’s a big red button at the top right of the community. Also on desktop you can see all the communities on the instance in the communities button at the very top, next to the instance logo, it’ll be a bit quicker to mass block by just going down and blocking each community you don’t want to see, but you still have to do it one by one in each community. And you can just subscribe to a bunch of stuff and set your default settings to sort by what you’re subscribed to.