Always told people to jump straight into a language, but your story makes me admit that was wrong.

My uncle got really into woodworking videos during lockdown, like 200 hours of them, and he never built a single thing. At some point watching becomes the hobby and that's fine as long as you know that's what's happening. Forty hours in 3 months is basically one hour a day, which is way less than most people spend on Netflix, so I wouldn't sweat it unless the note on your phone is stressing you out more than it's teaching you anything.

That 3-4-5 triangle in the apron pocket is the real deal, I keep a small one in my pouch for the same reason. Diagonals will lie to you on a racked box, so I check square first then verify with the tape.