I can not navigate something in modern versions of CLR

.NET Framework 2 – 3.5 is CLR 2

.NET Framework 4 – 4.8 is CLR 4

In which version of the CLR is executed .NET Core 1, 2, 3, and .NET5 code 1, 2, 3, and .NET5?

Answer 1, Authority 100%

in .NET Core version CLR is the same with the version of .NET Core. CLR updates are manufactured with standard library updates. If we talk about the Environment.version property, then before version 3.0, it returned the fake 4.0.30319.42000 for reverse compatibility. Starting with 3.0 It Returns the real version .NET Core , for example 3.1.x for .NET Core 3.1. Microsoft.netcore.app NUGET package from the .Deps.json file is technically taken.

Assembly version in metadata (.assembly directive in IL) For some standard libraries, it remains 4.0, apparently also for backward compatibility, since this version is used to resolve dependencies using a strict name. The file version for some DLL, which is displayed in the properties of the file in the explorer, also mainly remained 4.x, but this value does not affect anything at all.

Answer 2, Authority 200%

.net Core 1, 2, 3, and .NET5, all use CoreClr.

.NET Core and .NET 5+ Releases Have A Single Product Version, That Is, There Is No Separate CLR Version.
CLR VERSIONS

also:
introducing .net 5