It does not apply to servers running in, say, Canada¹. Or China¹. Or South Africa¹. (If you try to claim European law is extraterritorial to non-European citizens, be prepared for the Nelson Muntz meme.)²

The very nature of the protocol in use makes any content anywhere on the Fediverse, no matter what the software, distributed. (It's almost like that's the very point of it! Almost...) And it could well be distributed into a jurisdiction where the GDPR is best used as toilet paper¹. If this bothers you, fuck off back to sites hosted entirely in Europe where the GDPR holds sway.²

Only wait! That's not true either! Because that other protocol you're likely to be using—HTTP(S)—also allows anybody who has access to the site from anywhere in the world to store it without being beholden to the GDPR!¹ Oopsie! Better make sure that site blocks any kind of access from outside of the EU as well!²

Only wait! That won't work either because VPN's are a thing as well! I can be sitting here in China with my IP address coming at you from, say, the Netherlands. (It doesn't. It comes at you from the USA 'cause that's where my Great Firewall-crossing back door is hosted.) And again, any post you make, were I to go to your web site in Europe through my (currently-hypothetical) European VPN endpoint, could be stored and held permanently with the GDPR being able to do precisely a) Fuck and b) All to about it.¹ Because European laws are not, in fact, extraterritorial to non-EU citizens, no matter how much wanking the EU parliament does about it.²

So it sounds like you should just shut off your Internet access. Or, you know, you could post knowing the reality of the world and moderate your content accordingly.

¹ Note: I am emphatically not saying that the GDPR is a bad thing. I think the GDPR's goals are laudable. It's just that the GDPR is ludicrous in the face of how literally every piece of technology used in web sites of any kind actually works. It is a regulation that is a nice idea but that has absolutely no meaningful way to get enforced. As the EU will find out over the years. Hopefully not the really hard way.

² Any claim of EU legal extraterritoriality is risible and needs to be rebuffed in the strongest possible way up to and including punching EU politicians who claim it in the face with a spiked gauntlet.