Referencing .NET6 application from .net framework 4.8 app

Question

I'm trying to make references between my projects, two of them are in .net 6 and the third is my old project, in .net framework 4.8. Upgrading it is not an option for now. I'm in a context of an hexagonal architecture implementation. So:

ProjectLibrary1 (core): .net6 ProjectLibrary2 (infrastructure): .net6, reference ProjectLibrary1 Framework: .net 4.8, reference ProjectLibrary 1 and 2

Here my csproj:

ProjectLibrary 1 & 2 (updated after the comments):

  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

Framework: Screenshot of my config in vs studio

The problem:

I have errors with the version of C#. It seems like it compile for .net 6 (with global using for example), but I have errors.

Errors "project targeting 6.0 can't referenced by project targeting 4.8"

I would highly appreciate some help, I tried a lot of solutions but it didn't work.

Edit:

---

To summarize the answers I made:

The idea behind this architecture is to migrate the code step by step into new modern and cleaned application. We have a huge codebase, a huge technical debt and no budget to rework all the app. So my idea was to use modern apps and migrate the actual code base, to end with a clean architecture made of a "modern" core and an "old" framework. What would you advice in my context?

In my apps, I already have projects shared between do.net 4.8 and do.net core 3 projects. Why would it be possible with core 3 and not 6? Both of them have compatibility with do.net standard 2.0, according to this page ( https://learn.microsoft.com/fr-fr/do.net/standard.net-standard?tabs.net-standard-2-0 ).

Answer 1

To my knowledge, this is not possible, you can only reference a do.net framework or do.netstandard project from your 4.8 framework project.

Answer 2

You can't have both TargetFramework TargetFrameworks . You should either have TargetFrameworks with both .NET6 and .NET2.0 , or a single TargetFramework with .NET2.0 .