Sign in with Microsoft
Why Hexa Client asks for your Microsoft account and what it can see.
You need a Microsoft account that owns Minecraft: Java Edition. Hexa Client does not support offline or unpaid accounts.
You sign in on Microsoft's own page: Hexa Client never sees your password. It only receives your Minecraft name and UUID, and your Minecraft access token stays on your computer.
If the launcher or the website says sign-in is "not available yet", Microsoft is still reviewing Hexa Client. It starts working by itself once approved; there is nothing to do on your side.