Just a final update from my side (living in Germany):I got a working replacement mainboard (part number: 90MB14L0-M0XCN1) after a bit of back and forth. It needed two tries (=shipments) of mainboards since I got a used mainboard with the exact same i...

Sadly I'm experiencing the same issue: after upgrading to a 4070Ti the PC just randomly black screens. Setting maximum performance mode in the Nvidia control panel does mitigate the issue, however the system can still black screen before Windows even...