Online mode was disabled on my Minecraft: Java Edition account, and there's no way to...

Good point, I didn't try this. Although it bothers me to lose my configuration, I can't say I tried everything if didn't do such a thing.

I won't do it right now but I'll keep you up to date.

Thank you for your time and your help!

Hippolyte

Did you try to uninstall and install again both Minecraft and MultiMC after your account was given permission?

Exactly! That's what he did. I thought that would solve the problem, but nothing changed and it's been 2 weeks I've been trying to figure out why nothing can help it.

Hippolyte

Are you playing it using Xbox App on PC?

You could try to do the following (if not done yet):

- Completely uninstall Minecraft Java Edition;

- Then, completely uninstall Xbox App and Xbox Companion App (if you have both);

- After that, Press Windows + R and type in "regedit". Press enter;

- Search for HKEY_LOCAL_MACHINE\System\CurrectControlSet\Services;

- Delete "GamingServices" and "GamingServices.net" (if they're still there);

- After that, click on Windows (or press Windows key on your keyboard) > Search for Credential Manager > Windows Credentials. Search for Xbl|DeviceKey, click on it and then Remove;

- On your PC settings, Open Settings then System -> Apps -> Apps & features -> look for Microsoft Store and click it. The advanced options link will appear. Click on it. On the next page, click on the Reset button to reset Microsoft Store to default settings;

- Restart Windows;

- Install Xbox App (and Xbox Companion App if you use both);

- Open Xbox App and login to the correct Microsoft/Xbox account;

- Finally, Install Minecraft Java Edition.

See if these steps can help fix it, my friend.

When you get time, please try it and let me know, my friend.

You're welcome. Best Regards.