Edit: I realize I overlooked the "like 3Blue1Brown" prereq, instead sharing a list of the educational/interesting channels I find worthwhile. The most like 3Blue1Brown will be the PBS ones (especially SpaceTime), MinutePhysics, and Mathologer, for using diagrams to convey abstract concepts.

PBS Space Time and Eons are both awesome:

* PBS Space Time, covers cosmology and quantum physics:

https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g

* PBS Eons, for geology and paleontology:

https://www.youtube.com/channel/UCzR-rom72PHN9Zg7RML9EbA

* Smarter Every Day, Destin's enthusiasm is contagious:

https://www.youtube.com/user/destinws2

* Extra Credits various topics (video game design, History, and recently history of Sci-Fi) are great:

https://www.youtube.com/user/ExtraCreditz

* Today I Found Out is just on this side of clickbaity, and is this age's "Ripley's Believe It Or Not", but still interesting and more importantly well researched:

https://www.youtube.com/user/TodayIFoundOut

* Crash Course, of course:

https://www.youtube.com/channel/UCX6b17PVsYBQ0ip5gyeme-Q

* Gaming Historian, for some insight into the making of systems that formed my (and earlier) childhood:

https://www.youtube.com/channel/UCnbvPS_rXp4PC21PG2k1UVg

* Minute Physics, whose latest few videos made Special Relativity understandable to this peon:

https://www.youtube.com/user/minutephysics/videos

* Practical Engineering, for some insight into civil engineering topics that we take for granted:

https://www.youtube.com/channel/UCMOqf8ab-42UUQIdVoKwjlQ

* Real Engineering, for insight into various other mechanical engineering topics:

https://www.youtube.com/channel/UCR1IuLEqb6UEA_zQ81kwXfg

* Standup Maths, host Matt Parker was the first to make maths approachable for me again (before 3Blue1Brown took the lead):

https://www.youtube.com/channel/UCSju5G2aFaWMqn-_0YBtq5A

* Steve Mould, who covers various topics both mathematical and physical. You may have seen that gif of him demonstrating the "levitating" siphoning "pearl necklace" (also a friend of Matt Parker, above):

https://www.youtube.com/channel/UCEIwxahdLz7bap-VDs9h35A

* The 8-Bit Guy, for some history of early home computer systems:

https://www.youtube.com/channel/UC8uT9cgJorJPWu7ITLGo9Ww

* Numberphile, the second-greatest math channel (after 3Blue1Brown), whose recent video finally made me take the Golden Ratio seriously, rather than an architectural gimmick/conspiracy theory:

https://www.youtube.com/user/numberphile

* Mathologer, another good math channel (but I must sheepishly admit I prefer 3Blue1Brown... sensing a pattern here?):

https://www.youtube.com/channel/UC1_uAIS3r8Vu6JjXWvastJg

* Periodic Videos, for chemistry and physics, often featuring the iconic Dr Martyn Poliakoff:

https://www.youtube.com/channel/UCtESv1e7ntJaLJYKIO1FoYw

* NileRed, for some homegrown chemistry, I particularly appreciate the candor of the approach and results:

https://www.youtube.com/user/TheRedNile

Not quite as much "educational", but still very very good:

* Every Frame A Painting, now finished, but a great explanation of what makes good cinematography:

https://www.youtube.com/channel/UCjFqcJQXGZ6T6sxyFB-5i6A

* NoClip, long-form documentaries about the making-of video games. Danny O'Dwyer is a treasure:

https://www.youtube.com/channel/UC0fDG3byEcMtbOqPMymDNbw

Apologies for the link spam, this list turned out longer than I expected as I went down my subscriptions, and I've probably missed a few worthy ones!

Edit the final:
I discovered many of these channels through referrals from others I was watching, including from the twitter feeds of the authors. Turns out the educational landscape on YouTube is a well-connected graph!