Could be a driver but it is a good chance it is hardware or a setting that needs to be configured.
Since it shows up starting into Windows and when idle could indicate either a defective GPU card or the GPU Card is overheating. Overheating is one of the main reasons for Artifacts besides Overclocking the GPU card. Another is defective vRAM on the GPU Card. Also a weak or under-powered PSU can cause artifacts to occur.
Install the latest RX5700 AMD Driver from here: https://www.amd.com/en/support/graphics/amd-radeon-5700-series/amd-radeon-rx-5700-series/amd-radeon-...
Once installed, Stress test your GPU card and check the Temperatures, voltages and PSU Outputs to the GPU Card. See if it crashes or develops Artifacts while stress testing it. If you start seeing Artifacts, what is the temperature of the GPU card?
I heard that Furmark Fuzzy Donut is a good Stress Testing software to check for Artifacts and instability issues. But it does put a lot of stress on the GPU card. I prefer to use OCCT personally since it also stress tests the PSU.
You might need to use AMD Wattman in Radeon Setting to change some of the parameters of the GPU card to see if that helps. One setting is to put the Power level to 50% and see if it helps stabilize the GPU card.
