Tech channels for keeping up to date: LinusTechTips, Techlinked, Science Studio

Tech channels that go in-depth on various topics: GamersNexus, Actually Hardcore Overclocking, Computerphile, LiveOverflow

Math:

3Blue1Brown

History:

Shadiversity, The Armchair Historian

Futurism:

Isaac Arthur

Politics:

Aydin Paladin

Videogames:

Bellular News, Digital Foundry

Electronics:

EEVBlog

Guns and other weapons:

hickok45, ForgottenWeapons