Significant for some, less so for others.

The games with the most problems tend to be multiplayer titles with aggressive client-side anti cheat. For me, I only play a couple of online titles like Deep Rock Galactic, which are co-op and work fine, and which I wouldn't miss all that much even if they were broken. Most of my gaming is single player, and if it turns out a game is in the unlucky 10 percent then I can just move on, because there's plenty more on my wishlist.

So, it really depends who you are. For some people that 10% might cover the entirety of what you want to play, which is a huge problem. For others, they might barely notice.

It might be. But then again only 90% of Windows games run on Windows to begin with ¯\_(ツ)_/¯

Give it time and Microsoft will soon require every Windows user have a golf ball in their throat when using Windows.

macOS wants a word with you haha