As simple as possible, but not any simpler. Science and technology updates and summaries: https://www.youtube.com/@SabineHossenfelder

https://www.youtube.com/@scottmanley

http://www.youtube.com/@Millennium7HistoryTech

https://www.youtube.com/@AppliedScience

https://www.youtube.com/@BreakingTaps

https://www.youtube.com/@Coreteks

https://youtube.com/@drbecky astronomy

Aging Wheels - A car channel with a focus on quirky cars and EV hacking. Amazingly fun scripts and good editing, deserves way more attention.

James Channel - An offshoot of Dankpods (a more famous channel) with a focus on obscure games/consoles and electronics hacking.

Road Guy Rob - Some of the most impressively made and presented educational topics about transportation infrastructure. Much less "preachy" and more interesting than other similar channels.

One of my personal favorite channels for relaxation is this gaming channel:

https://www.youtube.com/@BinaryVigilante

I cannot believe how many good videos this (down to earth) guy has uploaded (1.1K) and for how long he has been doing it, yet still has hardly been noticed.

ItsMarloe is another good gaming channel. He does Minecraft without the screaming, brainrot editing, and semi-scripted server drama that is so prevalent.

https://youtube.com/@ItsMarloe

BlueMaxima is similar but stands at 2.1k videos: https://youtube.com/@BlueMaximaC099

https://www.youtube.com/@HaveYouSeenThisChannel but only the least viewed videos. Half the videos (the most popular) are reaction compilations, but I find the less popular actually more creative and interesting.

Dunno what your definition of underrated is. In case you mean "under a million subs", Bringus Studios is worth a watch.

https://youtube.com/@BringusStudios

Shawn Charland: https://www.youtube.com/@skyindustries/videos