Considering that you have 20 years of experience maybe you would find interesting Knuths "The Art of Computer Programming" books (sometimes referred to as TAOCP) although it is a bit "hardcore".
IMHO a must-read is SICP ("Structure and Interpretation of Computer Programs")
"Dragon Book" ("Compilers: Principles, Techniques, and Tools")
Ofcourse there are plenty of online courses on the internet as others mentioned here
I like this resource: https://teachyourselfcs.com
Another comment mentions teachyourselfcs.com. I can vouch for that. I am a chemical engineering undergrad who taught himself computer science mostly using those resources.I had fair bit of interest in becoming a machine learning researcher and I had good enough experience in programming, so wanted to learn CS in depth.
Incidentally, I started a company called Primerlabs(https://Primerlabs.io) which creates self paced conversational CS courses to learn on your own. Although there are only two courses now.
So, I will say go with teach yourselfcs. Other listicles are too much info, Imho.