Tried disabling the iGPU (Intel HD Graphics 630) to see if it causes the problem and it actually did. Problem is, that this is not a solution. Using the other GPU consumes alot more unnecessary power and the laptop doesn't last at all.
So it has something to do with the integrated graphics card from Intel. Don't know if it conflicts with something that changed during the update because of Intel or because of Microsoft but this is clearly a software problem that I shouldn't expect to find in a brand new device ...