I have been exploring Kbin a little bit and can answer some questions.
ActivityPub is a protocol for sharing content. That content can be of multiple types like posts, threads, blogs, videos, microblogs, etc (I forgot the exact names of those types so the names might be off). On Lemmy we have communities, which are comparable to subreddits, that are hubs for ActivityPub content of the thread type. Mastodon is build for microblogs, which are similar to tweets.
Kbin is indeed similar to Lemmy, as it also runs on ActivityPub content, but apart from having communities (which they call magazines), you can also post and read microblogs there.
So if you like Lemmy but you're also on Mastodon or are interested in that, maybe Kbin is more suitable for you.
This is not what this is about, YouTube will be implementing a three-strikes policy if you are using ad blockers: https://www.theverge.com/2023/6/29/23778879/youtube-videos-disabling-ad-blockers-detection