It depends on the application.. you can try running your assemblies through MoMA (mono's migration tool) to see what gets flagged. A lot of the enterprise classes that are tied to windows obviously don't work... There's also no support for WPF iirc, though there is some Silverlight/Moonlight support, but that's another story.

If you're doing web/api services, then mono/.net core are serviceable. Though I would recommend that you have CI/CD setup to use linux/mono if you are going to target that platform... for the most part if it works in linux its' going to work in windows, not so much the other way around.

Take this with a grain of salt, as I've been mostly node.js for a couple years now, though the progress with .Net core and VS Code have my interest.