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3blue1brown is an amazing intro to mathematics and does an amazing job explaining hairy math concepts with great visuals etc

Cosign. He's a fantastic explainer.

Louis Rossmann does in depth component level Macbook motherboard repairs and circuitry explanations. If you're into good (and comedic) explanation on mechanical stuff, I highly recommend AvE and This Old Tony.

Eevblog

Smarter every day

LEMMINO

Socratica

Captain disillusion

Ahoy

Khan Academy

Moshix

Historia civilis

Computerphile

jpkiwigeek

Ippsec

Pydata

Deviantollam

Lockpickinglawyer

Numberphile

Strafefox

Company Man

Accursed Farms

Civvie11

... In no particular order. YouTube is great.

I would add thesignalpath and mikeselectricstuff to the list. Much more advanced, but very good to learn professional PCB design

Applied Science channel is worth mentioning.