Minecraft Java is no longer in my account

Do you have another Microsoft account though? Because if the game is not on there, it could be on another Microsoft account when you had the migration. Try other accounts that you have just to check.

You already migrated your account to Microsoft and that also will migrate your game to Microsoft store.

Try this:

simply open the Minecraft launcher, click accounts and sign out. Login using Mojang account (this will fail if you have migrated already), and then re-login using Microsoft account. This will 'reset' (without loss of data) the game back to normal allowing you to play offline.

So I logged out of the Microsoft account, I attempted to log in with my old Mojang account, it failed, and then I logged back in with my Microsoft account.

And, again, I'm on Linux. I have no Microsoft Store. Tried looking at the Microsoft Store website, but I didn't get anything useful from there either.

It talks about the Microsoft Store, and probably Bedrock. I play Java and I run it on Linux.

I only have one other Microsoft account I haven't used in ages, but, just to be sure I'm not insane, I checked that one too before asking this question.