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