Plenty of people are delighted when the community they forgot they subscribed to months ago suddenly has new content!

https://lemmyverse.net/communities

Lemmyverse will let you search every community hosted by Lemmy instances that share data with it, which is most. If you set your home instance before you start clicking links they’ll open on your home instance so they are easier to subscribe to.

Here’s a recent post I put together with some more resources:

https://walledgarden.xyz/post/1600683

Edit- Also worth mentioning the Voyager interfaces offer a solution for this.