I highly recommend the Handmade Hero series to folks in his situation. Casey has put up an absurd amount of material for everyone for free.

https://www.youtube.com/playlist?list=PLnuhp3Xd9PYTt6svyQPyR...

https://guide.handmadehero.org/hmcon/

https://guide.handmadehero.org/

https://handmade.network/forums