AstroworldMC is in closed beta right now, so only players on the beta list can join. Everyone else can play from the public launch.
The Java IP is play.astroworldmc.com. Add it to your server list in Minecraft Java Edition 1.21.11.
For Bedrock (Windows, phones and tablets): the same address play.astroworldmc.com on port 25571. Geyser handles the conversion. Xbox, PlayStation and Switch don't let you add your own server, so consoles can't join directly.
The server runs Minecraft 1.21.11. Older Java versions can't connect.