The part with the "You need 1903 version" is with a little* on the end. It turns out, that the problem, when upgrading to a higher windows version, a certain driver for the pci bus gets updated (or at least that's my understanding). After swapping out a certain file (pci.sys, there is some info in the thread) everything starts working again on the latest build.
Yes there's a specific subset of 1903 that works. If you update to one of the newer versions of 1903, even download one of the newer 1903 ISOs, or certain Windows updates it will install a new pci.sys that will likely give you the Error 12. There's a few tricks. 1) Stick to the early 1903 or 18xx builds that worked 2) Upgrade to newer 1909 or beyond, but manually replace the pci.sys in C:\Windows\system32\drivers or 3) wait for new Windows update / get Windows Insider fast update where they seemed to have fixed the pci.sys error 12 issue again (and possibly improved eGPU utilization?)