For machining, Stefan Gotteswinter is high on my list. He's beyond awesome. Abom79 for the hands-on heavy stuff, This Old Tony because the guy is just hilarious . Blondihacks for showing how experience trumps raw talent.
CuriousMarc is fantastic. His AGC restauration series is gold. Watch it if you haven't already.
Scott Manley for everything I ever wanted to know about space travel
The Signal Path because it is way beyond my skill level yet cool to watch.
Louis Rossmann for the rants and for showing how to repair consumer electronics at component level.
FranLab for the vintage electronics stuff, not for the whining over YT.
Mark Rober, for the annual Glitter Bomb updates. Not for Team Trees.