It's not that complicated. ASP.net Core 2.2 and earlier was targeted at .NET Standard, so could run in any CLR (CoreCLR or Framework or even Mono, though I don't know how supported mono was). Asp.Net Core is actually just a csharp library like everything else.
It's still in support, and led to one of the most confusing release announcements in history: https://devblogs.microsoft.com/dotnet/servicing-release-advi...
ASP.NET Core 2.3 does go end of life in April however: https://devblogs.microsoft.com/dotnet/aspnet-core-2-3-end-of...