The .NET Framework 1.x runtime is no longer supported, and the .NET Framework 2.0 runtime (used by v2.0-3.5 applications) won’t be supported after 2029. They are slowly abandoning support for old apps.
(Yes, if you fiddle with the config file they might work on the .NET 4.0 runtime. But that’s not something a typical user can/will do.)
It keeps classes for backward compatibility, not assemblies. Some code still didn't migrate from them to not cause gratuitous churn. Also it's web scale, because untyped collections can hold values of different types just like javascript.
What are you talking about??? .NET never got abandoned! If anything its hit a very high bar now. Its one of the top frameworks to build an app across platforms.
They're referring to (I hope), the .NET Framework which is Windows-only and the last/latest version being 4.8. It should live a very long life, as Microsoft server infrastructure is built on it (SharePoint/Exchange).