So, I updated to the new Windows 10 May 2020 Update aka version 2004, and decided to check device manager what's going on with the GPIO-driver, because the latest drivers would be blocked on version 1909 (See thread AMD GPIO Controller blocked (Code 48) )
Well, it's working now, but it's using some ancient driver 126.96.36.199 from 2017.
So, I just re-downloaded the latest chipset drivers (2.04.04.111) and tried installing them.
Everything started fine, it said installing, but then suddenly just stopped and said installation failed, no error messages. I've attached the installation log, which shows error code 1603 ("MSI (c) (60:10) [14:14:28:438]: MainEngineThread is returning 1603")