Hi, my name is Julian. Since this is a public forum made up mostly of fellow gamers and users like you and me, all we can offer are guidance and suggestions. I'm sorry you're experiencing this issue.
This usually means there's a temporary issue with Microsoft or Minecraft's authentication servers. You can check the live server status here:
https://support.xbox.com/xbox-live-status
If the servers look fine, try these steps:
- Restart your game and launcher.
- Log out and log back in to your Microsoft account.
- Make sure your system time and date are correct.
- You can also try rebooting your PC or router.
If none of that works and the issue continues for hours, reach out via:
https://help.minecraft.net/hc/en-us
Please let me know if it worked or not and I would be happy to assist you further. Thank you!