The shift is slow, but it has been ongoing for years, and is pretty much wrapping up now. .NET 5 was released in November, 2020 and that was the "beginning of the end" of the shift over.
For what I do, it's not really "Windows development" in any meaningful way. It is business functionality with HTTP, message queues etc, developed on mostly Windows laptops, and deployed to mostly Linux instances on the cloud. Not that the host OS is something that we have to think about often.
For this, .NET 3.x "the full framework windows only version" services are regarded as very much legacy, and I wouldn't go near one without a plan to migrate to a modern .NET version.
However, YMMV and people are also making windows desktop apps and everything else.