This you? https://isdotnetopen.com/
After .NET Core I was one of the people that really thought "maybe Microsoft has changed at least in the .NET division, let's not be prejudiced, if they want to make FOSS let's give it a try". But of course they showed their hand and I'd have to be a fool to believe this is a platform worth investing myself in.
It's even killed my enthusiasm with F#, despite it almost growing into its own thing after how much MS has neglected it.
Am I reading that right... no debugger..?
That can't be the case?
You can download the official .NET debugger but its license only permits you to use it with VS and VSCode.
Luckily, there are various third-party debuggers available. E.g. from Samsung (MIT licensed) and Jetbrains (proprietary for their IDEs).