The issue with mastodon communities is that they don't use the same type of fediverse tools. You could maybe follow people from mastodon, but the apps or Lemmy/kbin will need to implement a compatibility with those fediverse websites.
To follow communities outside your instance it's a bit less optimised currently as the instances don't scrape all the communities from other servers.
So to find them, either someone else had to search it and subscribe to the community for the server to show it when you search for them, or you'll have to show the server where the community is :
For example a community from your instance : !apolloapp@reddthat.com
You can notice that I put a ! Then [community] and @[server address].
You will often see this presentation under the community name when clicking on a community : !apolloapp This is what that means.
If you were on another instance, to find the apolloapp community from reddthat.com, you'll need to search for either : !apolloapp@reddthat.com Or https://reddthat.com/c/apolloapp
I don't know if apps are able to search like this, so you may need to go on your account in a browser and search from there.
Also as stated in another comment, there are websites to search for communities, like Lemmyverse.
However you can find communities to replace the reddit ones here :
https://www.quippd.com/writing/2023/06/15/unofficial-subreddit-migration-list-lemmy-kbin-etc.html
And
Well there are multiple sides to this. There isn't a single it's good or bad.
Reddit got very popular, and the upvote/down vote was a part of it.
A very useful thing of this feature, is the ability to hide trash and get good content more views.
However the community isn't perfect, and some types of content can win over others, and often that winning content isn't useful, as it's just jokes or "funny" content.
If you were to sort by controversial in the reddit comments, and communities, you'll often find trash and useless content. Comments or posts alike. However it's. Not always the case, and sometimes legitimate content just gets down voted because people did not understand it or were just against that opinion.
In my opinion, if reddit were to remove the impact of the up votes/down votes and just put things as random, the content would be horrible with trash everywhere. But the little accounts may have a bit more chance to get up votes.