The issue is one of licensing, not technology. There’s all kinds of patents in the space, and using free codecs could still infringe them. DirectX doesn’t have the same patent protection. I believe in theory you could make a fully open source Linux native version of DirectX.
For more info from someone who knows more than me, see here.
Linux may very well not be for you, but using Arch first is like jumping into the deep end to learn how to swim. It’s no surprise you’re drowning. I’d recommend you try a gaming-focused distro like Nobara before you go back to Windows for good.