UPDATE September 30, 2020: AMD has released driver version 20.9.2 which fixes the crash with X-Plane and Vulkan. See the AMD release notes and download the driver here.
Enabling Vulkan rendering in X-Plane 11.50 with AMD driver version 20.8.3 can cause crashes. As of Sept. 1, 2020, we recommend using the previous driver (version 20.8.2) until a newer fix is released by AMD.
The Radeon Software Adrenalin 2020 Edition 20.8.2 driver can be downloaded directly from AMD at this link:
Scroll down the page to find the “Radeon Software Adrenalin 2020 Edition 20.8.2 Driver” link for your version of Windows. Click the link to download the installer. Run the installer and then restart your computer. At this point you can start X-Plane, re-enable Vulkan in the graphics page of the settings screen, and restart X-Plane so the driver change takes effect.