If your .NET Framework projects are in the old csproj style, first convert them to SDK style - no changes to the target runtimes or dependency versions. For asp

If your .NET Framework projects are in the old csproj style, first convert them to SDK style - no changes to the target runtimes or dependency versions. For asp.net, winforms, or wpf apps, this is usually the hard part. Once the app is working with SDK style projects, then try changing the runtime to netcoreapp. Often it just works; if it doesn't, you'll get useful error messages.