You can't assume that we're all using DirectX. Some of us aren't using Windows and so don't (directly) have the option of DirectX. On Linux-based operating systems, the default is Vulkan and the alternative is OpenGL. Yes, we can install the Windows version and play via Proton (which would probably avoid the errors due to the game using DX11 but dxvk being involved), but that's sub-optimal.
If your mod can cause Desired shader compiler platform 18 is not available in shader blob to appear in Player.log, your mod will cause rendering errors for some of us (me included) and you need to check that your mod properly supports Vulkan.
You can't assume that we can all use Vulkan. I can, but some people are playing Valheim on hardware old enough not to have support for that and have to use OpenGL instead.
If your mod can cause Desired shader compiler platform 15 is not available in shader blob to appear in Player.log, your mod will cause rendering errors for some of us (not me) and you need to check that your mod properly supports OpenGL.
I've tested a few mods for these errors. There seems to be a mix: some don't properly handle OpenGL only and others don't properly handle OpenGL or Vulkan. Rendering errors tend to be that objects without transparency are rendered in one colour, bright, and without lighting effects and that decals (essentially, flat objects with transparency) are rendered in one colour, without the intended transparency, and acting as colour filters on whatever's viewed through them.
Source: https://www.reddit.com/r/valheim/comments/18cmzbw/mod_authors_graphics_apis_crossplatform_support/
