Ok, I finally figured out how to be able to run almost all my Steam games on my laptop.
I have a quite unusual setup; I have two video cards on my laptop, one is Intel and the other is NVIDIA RTX 2070. I also have a third external video card, an NVIDIA RTX 3090, and almost everything runs on my external video card.
So the command line string to run Steam is this:
MESA_VK_DEVICE_SELECT_FORCE_DEFAULT_DEVICE=0 MESA_VK_DEVICE_SELECT=10de:2204 DRI_PRIME=2 DXVK_ENABLE_NVAPI=1 DXVK_LOG_LEVEL=none DXVK_NVAPIHACK=0 VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/nvidia_icd.json DXVK_FILTER_DEVICE_NAME="3090" DXVK_HUD=fps,gpuload,compiler /usr/games/steam %U
MESA_VK_DEVICE_SELECT_FORCE_DEFAULT_DEVICE=0 MESA_VK_DEVICE_SELECT=10de:2204 to force Vulkan apps to use my RTX 3090. So Windows Vulkan-based games would be able to run: Detroit: Become Human and Sky: Children of the Light are using Vulkan.
Setting DRI_PRIME=2 will make native Linux-based games run on an RTX 3090.
The line DXVK_ENABLE_NVAPI=1 DXVK_NVAPIHACK=0 VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/nvidia_icd.json DXVK_FILTER_DEVICE_NAME="3090" is needed for Windows DirectX 12 based games.