The username I have hasn't been taken but I can't create a profile.

I was reinstalling Minecraft onto a new PC through the new launcher and I logged in with my Microsoft account now that I transferred my Mojang account to it. I try to reinstall Java but I am told I have to select a username that's available.

What I expected to happen was...:
I thought I would just type in my name and be able to go on with downloading.

What actually happened was...:
I typed in my username and see that no one has taken it, but whenever I click "Create Profile", a popup in red tells me "Failed to create profile".

Steps to Reproduce:
1. Reinstall Minecraft.
2. Attempt to reinstall Java.
3. Type in a username that is accepted and click "Create Profile"