MinTTY is the terminal emulator that comes by default with Git for Windows. It has known issues with gh's ability to prompt a user for input.
There are a few workarounds to make gh work with MinTTY:
Reinstall Git for Windows, checking "Enable experimental support for pseudo consoles".
Use a different terminal emulator with Git for Windows like Windows Terminal. You can run "C:\Program Files\Git\bin\bash.exe" from any terminal emulator to continue using all of the tooling in Git For Windows without MinTTY.
Prefix invocations of gh with winpty, eg: "winpty gh auth login". NOTE: this can lead to some UI bugs.