For (2), this is often misunderstood and mistated.
The JVM includes no GUI framework. .NET also includes no GUI framework. .NET happens to have a specific framework for Windows. But just like the JVM, there third-party GUI frameworks such as MAUI, Uno, Avalonia, and others.
So no, there's isn't a "large part" of .NET that isn't cross-platform.
> 3. the level and quality of official tooling provided for Linux and macOS is incomparable to their Windows offerings
The JVM includes no GUI framework. .NET also includes no GUI framework. .NET happens to have a specific framework for Windows. But just like the JVM, there third-party GUI frameworks such as MAUI, Uno, Avalonia, and others.
So no, there's isn't a "large part" of .NET that isn't cross-platform.
> 3. the level and quality of official tooling provided for Linux and macOS is incomparable to their Windows offerings
What are you referring to here?