>And are there any good examples where teams actually migrated away from 4.x or 8.x successfully
Sure, at my former workplace they migrated one of the products (a document processing platform) from .NET 4.5 to .NET 8.
It's quite a lot of work to do something like that and most companies who have old products on .NET 4 don't care to update them because they still work. Many are still adding new features to old .NET 4 codebases.
Many will only upgrade if Microsoft deprecates .NET 4 and stops providing updates.
Sure, at my former workplace they migrated one of the products (a document processing platform) from .NET 4.5 to .NET 8.
It's quite a lot of work to do something like that and most companies who have old products on .NET 4 don't care to update them because they still work. Many are still adding new features to old .NET 4 codebases.
Many will only upgrade if Microsoft deprecates .NET 4 and stops providing updates.