You can try this course in Udemy I started it few days ago and it is goes very well
https://www.udemy.com/course/developing-a-multithreaded-kernel-from-scratch/?srsltid=AfmBOoosOpjhTQUluEOaewKJnXf7fBvsFgLkkQ4g-_egGFFRP5N2cFWU&couponCode=ST19MT280525G1