The method I've tried is...
1. MS Store initialization.
2. Delete MS Store cache.
3. Update windows and graphics drivers.
4. Reboot and re-login.
I've tried everything, but the same error appears.
(Minecraft Launcher is currently unavailable in your account. Make sure you are logged in to Microsoft Store and try again. If necessary, the error code is 0x803F8001)

This error occurs when executing Minecraft launcher, and the MS store is also logged in.
Also, the product is registered on Minecraft's official website, but it doesn't appear in my library in the MS store. (It's the same ID.) For your information, this error message is not captured, but only clipboard copy is possible.