Also having this problem.
Cura 4.0.0
Ryzen 2700X
Nvidia RTX 2080
32GB RAM
ASUS Strix X470-F motherboard
CPU, VRM and GPU are liquid cooled, temps are 50C or less.
I pulled my OC off the CPU and GPU still am getting blackscreened after about 30 minutes in CURA.
BIOS are updated and I have checked CPU voltage and made sure there isn't a power problem.