Yeah. There’s no wildcard call. One thing you could do to script it would be pull JSONs from https://data.lemmyverse.net - use one for the initial effort, then subsequent ones to track new communities. You’d definitely want to filter it - as you’ve noticed the vast majority of that 30k are dead or spam or something you wouldn’t want for one reason or another (e.g. communities from instances you’ve defederated from).
As for what bots do, it depends on how they were programmed I suppose. There’s a bonkers one on https://leaf.dance that just seems to crawl comments and subscribe to any ! links it finds, but there are others (I can’t remember their names) where it’s more of a manual job (the mods of a community submit the details to it).
Hello sorcerer. Please erase “Man, I feel like a woman” by Shania Twain. It annoys me anyway, but it not like it makes being a woman sound especially inspiring either (“Colour my hair, do what I dare” - woah, slow down there Shania!). Thanks.