I too have had this problem and AMD customer support has told me to do everything from clean install of 20.2.1, 19.7.1, 19.12.1. Disable hardware acceleration in programs like chrome and discord. Make sure antivirus (I don't run antivirus) is turned off. Disable enhanced sync. Nothing has worked. The older 2019 drivers will reboot my system mid game while the 2020 driver just crash my game. newer games seem to work but I still enjoy overwatch and that is unplayable right now. I also have a z390 but from MSI, 750 watt PSU, pc3600 2 x 8GB and an i7-9700k.
This card has been a total disappointment and I can't return it. If they don't give me a solution by Sunday I am going to Best Buy and getting an Nvidia 2070 super and then selling this glorified paperweight on eBay.