First, enable the multilib repo as per the other comment.
Then, to get Vulkan working properly on Optimus, install the following packages:
primus_vk vulkan-tools vulkan-icd-loader lib32-vulkan-icd-loader nvidia-utils lib32-nvidia-utils
After that, run vulkaninfo
- if you see info about your graphics card, you will know that Vulkan is working correctly. vkcube
is another app you can run to test Vulkan.
Also, according to ProtonDB, you'll need to set the following launch options in Steam for DotA 2:
gamemoderun %command% -novid -high -vconsole
XFCE + Chicago95 theme + some theme tweaks here and there