Modern .NET is legally owned by the .NET Foundation. It is MIT/Apache licensed with the exception of some debuggers in VS Code (which propably conflict with VS itself).
Granted, the .NET Foundation is not the Apache, Eclipse, Linux or CNCF Foundation and it is dominantly financed by Microsoft, but there are relative important peers like AWS or RedHat involved.
Plus now we have Jetbrains Rider. So there's an excellent non-Microsoft IDE alternative.
Rider is no joke. If you haven't used it or gave up on it a few years back, give it a shot. There are a few things it can't do like attach to managed modules hosted in unmanaged processes but it's a joy to code in.
The problem I see with .NET now (I did some tinkering on it via Unity) is that even though some of it is "open source", Micorsoft's grip is still pretty tight on it. Or at least it feels like that.
Given Microsoft's history I find it very difficult to "commit" to using the .NET framework for something real, because I feel I will be bitten back with the 'proprietary' aspects of it as soon as I go to production. It's a sunk cost that I cannot afford.
And it is not personal 'hatred' or anything given that I use VSCode as an editor and TypeScript itself comes from Microsoft.
I wish Microsoft would donate .NET to some 3rd party open source foundation (like what happens with all Apache projects, or LibreOffice, the MariaDB foundation, etc).