In the past, I was able to find more of these, but now they're just a small fraction of all the channels I subscribe to.
Brother Jake - Mormonism - 19k https://www.youtube.com/channel/UC0u7ZMWqkr7cKD_rvEXZUuQ
Ed's Auto Reviews - autos - 46k https://www.youtube.com/channel/UCNFJQbMjDfxc8pacVPhAtIw
Francis John - Oxygen Not Included - 55k https://www.youtube.com/channel/UCk6C1z_ErW4XssWUdDSfV7Q
Greg's Airplanes and Automobiles - planes and autos - 80k https://www.youtube.com/channel/UCynGrIaI5vsJQgHJAIp9oSg
Illinois EnergyProf - science - 61k https://www.youtube.com/channel/UCKH_iLhhkTyt8Dk4dmeCQ9w
Nick Zentner - geology - 28k https://www.youtube.com/channel/UC4szl4Ra1ZD3m80wJP40UBA
DarkAero - aeronautical engineering, composites, etc (45k subscribers) https://www.youtube.com/channel/UCPUZCBNrduwUsw_MTW-sDxw
Xyla Foxlin - maker channel (~99k subscribers) - https://www.youtube.com/channel/UCEn3fRj2e0mpqYsijxnzayg