Comment # 19 on bug 107296 from frido.ferdinand@gmail.com

Same problem, initially installed arch with an nvidia 970 card, later switched
to internal vega graphics on displayport with 144hz monitor now blank
(flickering) screen on boot. Details:

5.3.1-arch1-1-ARCH
ROG STRIX B450-F GAMING, BIOS 2801 09/18/2019
AMD Ryzen 5 2400G with Radeon Vega Graphics (Using displayport)
GeForce GTX 970

dmesg attached.