Learn WordPress course

Hello dears,

I run Image Matters (www.imagematters.me) which sell websites based on WordPress themes I buy from themeforest.net

I’ve been hiring freelance WordPress developers which is alright for me.

Lately I decided to learn WordPress on my own. (I already have a computer science degree since 1994; don’t know how much this will help me in my new endeavor).

Could you please advise me a FULL Learn WordPress Course on Udemy or any other platform that will allow me to learn developing WordPress themes (not from scratch)?

Thank you and be safe.

https://codex.wordpress.org

Thank you ki-themes,
To tell you the truth, I prefer to start with udemy (or any other platform) style tutorial with an instructor based one. Then once I know what I am doing, would go through text based tutorials.
Thanx a lot again,