You need Minecraft Bedrock and an Xbox account.
There is a version for Android and one for Windows.
It is your Xbox account name; the server needs you signed in to Xbox. The app shows a six-character code that lasts five minutes.
Add the server in Minecraft Bedrock and connect. We run 1.21 and up, always including the newest version.
Type /login with the code in the chat. The app opens on its own and your name becomes your @username.