The “OpenBSD version” is actually taken from the Linux sources. (See above).
And it works. 
I am currently cleaning up. I was able to Frankenstein a Debian 12 (Bookworm) on my Bananapi with Linux Kernel 6.10.6. But I used a wild combination of Qemu, Hacks, and your Bullseye release.
? Why not look into the sources or using the bookworm release from my gdrive and looking in the pipelines/build.sh how it is done?
Because it is more fun this way. 
Plus: Having a shell script that does the work for you is one thing.
UNDERSTANDING how everything is working together is another.