[Feature] MacOS Support

[IsSmallPigPig]

Before Requesting

• I found no existing issue matching my feature request
• This request is related to Millennium, and not a request for a specific theme/addon

Describe the feature you'd like!

Why we do

You know the Apple Company now are focus on Games on Mac, In recent Day The Cyberpunk 2077 is enable to run on the MacOS. So I think maybe a lots of users will use Steam on the Mac.But the Steam default theme looks so bad,We want to a third-party application to change theme.Please

Anything else?

No response

[shdwmtr]

It's somewhat in the works, It might be released in the coming weeks/months