The below should work as is:

  sudo apt install dotnet9 # or dotnet-sdk-9.0 if the repo doesn't have dotnet9 metapackage
  dotnet new console --language F#

There is also a package for Avalonia that lets you write GUI applications in F#: https://funcui.avaloniaui.net

I didn't use it 10 years ago but I've been using it for the last 4 years on mac and linux exclusively.

Microsoft seems to be prioritizing "cloud" on all their developer products (rather than just windows). I don't feel disadvantaged by NOT using dotnet on windows.

Vastly. You were probably using Mono. .NET is now fully cross-platform and very good at being so.

Very much so.