From a 20+ year old school player to another welcome back old timer

. As others have said CC has a good 30-day free course....which if you played 20 years ago you might be a bit above needing idk. But give it a look anyways see what you think. I had a look and but didn't take it.
You didn't say what format games and stakes you'd be playing.....
If you plan on starting with just micro cash I'd say just jump right in and get started at 2nl or 5nl both aren't that hard to beat even in 2026. Give the following Jonathan Little site a look it has preflop charts and lots of good free info available for you
https://www.mypokercoaching.com/. I'd also have a look at buying the following books Modern Poker Theory(heavily GTO based) but all the reviews say it's a great book and must read much like most the 2+2 publishing books you likely read back in the day. Also for your mental game I'd look at the following 2 books: The Mental Game of Poker 1&2 by Jared Tendler both also are consider really good and must reads. Whether you play MTT's of cash my advice above applies.
That's all I got best of luck at tables man.
Cheers!!!