You actually can't sign up on mastodon.social at the moment. I thought the same, all the instances are for weirdly specific groups I'm not in. You don't have this problem with email, there's no requirement to choose an email address that matches your political tendencies, sexual kinks etc.
I eventually chose fosstodon.org which seems like about the most vanilla thing that's open to new users and where I have a decent claim to being the right kind of person. I suspect a lot of people will look at the long list of furry-centric instances and conclude Mastodon is not for them. IDK, maybe that's considered a feature.
But it really is the same with mastodon. You don't need to find an instance that matches your political tendencies, furry niche, or whatever.
Just pick one that feels right. Maybe you are French or Korean and like a server in French or Korean, or maybe you feel very strong about politics: the make that a parameter. Otherwise just go for any "general" server.
Just like with email, people will generally just pick Hotmail, AOL, xs4all.nl, yahoo or email, without much thought. This is fine.
You can easily move later if you ever find a community that you wish to be part of.
That's exactly what I tried, and failed, to do. As far as I was able to discover, including via the site being discussed here, there are no such servers currently available for new signups.
I’m not convinced that this is a temporary issue - the mastodon servers seem to require relatively high upkeep (cost, cpu, and manual time) for relatively few users, which naturally leads to instances reducing/blocking new accounts and even just shutting down, which further exacerbates the load on other instances.
As I wrote in an earlier thread[1], this indeed is a problem. With mastodon.
But as numerous people replied, many alternatives are ready or wip. Many of them make hosting really easy. Since that thread I tried several. Gotosocial being my favorite, now.
So this too isn't fundamental. Because 'mastodon' is about much more than this one piece of software. It's a network, the fediverse. And you can easily host a near 1-1 mastodon alternative today on a cheap, VPS.
I eventually chose fosstodon.org which seems like about the most vanilla thing that's open to new users and where I have a decent claim to being the right kind of person. I suspect a lot of people will look at the long list of furry-centric instances and conclude Mastodon is not for them. IDK, maybe that's considered a feature.