I've built a GS rear wheel once
Thats helpfull
In my youth I raced bicycles, later I coached. I built dozens of bicycle wheels, got to a stage when I could lace and true a wheel in about an hour. Later I built motocross wheels for friends.
So I'm not a wheel building complete novice, right? The Beemer crossed pattern humbled me to submission - after hours and hours of trying to figure out the behaviour of it, being in contact with guys around the world who had experience with these wheels etc,I decided to attack it completely differently.
I measured all the spokes to be sure they are exactly the same length, and instead of trying to true the wheel through the rim behaviour I counted turns on the nipples, and it worked. I got a wheel within BMW spec.
This wheel got ruined as the hub fractured. I couldnt get a used hub anywhere so bought a complete wheel (used). The wheel I've built had a black anodized rim so I bought a set of SS spokes thinking I'll replace the rim in the newer wheel with my balck one but as all arrived I left it as it is - couldnt bring myself to dismantle a good wheel that I might not succeed in rebuilding...
I saw some wheels that were built with regular rims, I don't know where the spokes are from, maybe custom made? This could be a solution, and also can be converted to tubeless by sealing the spoke holes.