I'm also interested in running main-line Debian rather than the provided image on my Sipeed LicheePi 4A. It's a competitor to the StarFive VisionFive 2
I'm not sure how to help you, just encouraging you that there are others wishing for the same thing.
I was hoping to attempt in the next few weeks, and I'll update you with my process and results.
Thanks for your time and efforts!
-Thomas