Bluesky, a decentralized Twitter-like social network, is pausing new signups “temporarily” to try and resolve performance issues it’s been experiencing after Twitter introduced limits on the amount of tweets you can see in a day. Even though you still need an invite code to be able to join Bluesky, it seems that the influx of new users has been a problem.
It depends on the scale. At a small scale with only dozens of users, it’s super simple. However, to handle the scale of millions of users? Now we’re talking about a vastly more complicated system to create, since you need caching layers and other optimization techniques that are complex even for very experienced programmers.