announcements VS azurelinux

I don't think that works. That would alert you about the security alerts on the Security tab of the dotnet/announcements repo, which are empty, not about issues that contain information about .Net security issues.

.NET Core 2.0 Cryptography uses Apple Security Framework on macOS · Issue #21 · dotnet/announcements (github.com)

Yeah, it's a fun meme, but there have been a few nasty RCE vulnerabilities patched on .NET Core in the last couple years. Like this one: https://github.com/dotnet/announcements/issues/178

If you started receiving errors when pulling old versions of dotnet docker images (like the .NET 2.1), it's because Microsoft deleted them from Docker Hub on August 21st, 2021. That date is not a coincidence, the .NET Core 2.1 reached end of support in the same date. For more details take a look at the official dotnet announcement or also the dotnet blog. In my case, the error bellow was thrown in the stdout when pulling the microsoft/dotnet:2.2-aspnetcore-runtime image:

I'm not entirely sure what that means. We're done porting .NET Framework APIs to .NET Core / .NET 5. .NET Framework is what it is now, and .NET is moving forward with .NET 6+. If it is worth porting your code to .NET 6, it is. If not, then it isn't. Both can be good choices. .NET Core on Linux, however, is absolutely not preview.

They're even already producing their own Linux distribution, CBL-Mariner, https://github.com/microsoft/azurelinux

This became even more interesting as Microsoft started to open source core technology such as Powershell, the DotNET platform, their internal Linux distribution, and much more. All this hosting on GitHub also made sense acquisition wise.

Quite a few servers and network switches, actually.

Likely a recognisable ‘Windows’ GUI on-top of CBL-Mariner

Nothing new. For several years they already developed and maintained CBL-Mariner (Common Build Linux) https://github.com/microsoft/CBL-Mariner Which od a base for Azure Linux and other projects.