Disable Mac option|alt+key input special characters

Symptom

My Mac suddenly shows double quote character " when I type option+u in VS code to switch words to upper case.

Reason

English keyboard includes special character set.

Solution

Remove English keyboard and add Unicode Hex Input keyboard instead.

Reference

https://stackoverflow.com/questions/60870113/mac-generating-∆˚¬-characters-instead-of-executing-vscode-shortcuts-that-involve

How to type Æ, €, #, @, © and more special characters on a Mac
If you’ve moved from PC to a Mac, or are using a different keyboard to the one you are used to, you might be puzzled by the position of keys. If you’re hunting for Æ or €, wondering where @ is at, or just looking for an easy way to type mathematical symbols, accents and more, we’ve got you covered.