Books to 'learn by doing'? https://news.ycombinator.com/item?id=22299180
Hard-tech blogs to follow? https://news.ycombinator.com/item?id=23206259
Online compiler courses? https://news.ycombinator.com/item?id=23187239
An extra item that I like is : https://www.goodreads.com/book/show/1416932.Software_Fundame...
Knuth's books are considered classic. They are pricey though.
Maybe as a variation on this, you can find a Raspberry Pi project to try every week and discuss what variations/improvements each person did to the process.
https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/E...
You might find his other papers and notes interesting for your group.