Given the sheer SIZE of supermassive black holes and how quickly the formed post the big bang it seems there are great odds of SMBHs coming from some MEGA big stars that collapsed very quickly. Problem is to my knowledge we've never observed a star big enough to collapse INTO a supermassive black hole.

https://phys.org/news/2021-03-massive-stars-early-universe-progenitors.html#:~:text=The%20leading%20theory%20suggests%20the,into%20supermassive%20black%20holes%20today.

We would have to look back far enough to a now VERY distant galaxy to observe such a massive stars collapsing and merging. Hopefully JWST can confirm them!!

Regarding black hole stars: https://www.youtube.com/watch?v=aeWyp2vXxqA&t=609s

I think black hole stars could well be the origin of some of the supermassive black holes if a whole bunch could smash together!