Another 10/10 free course is Scotty West’s Absolutely Understand Guitar on YouTube. Filmed in the 90s and it’s still one of the best classes out there.
The NY Times Crossword archives past puzzles and it really helped me improve at Crosswords in general. The archive dates back over a decade and there are certainly days that I just really want to do a bunch of crosswords.
I suspect this combo of a new daily puzzle and the complete archive will be the winning implementation over time.