Issue with multiple target frameworks in Nuget Package: 'package_version' is not a valid version string. Parameter name: Version

I made a Nuget package which has 1 project in it that targets .NETFramework Version=V4.8 and V6.0.

It also has a dependency on another Nuget package being: Microsoft.Graph.

When installing the package on a .NET V6.0 project everything works fine, however, when installing the same package on a .NET v4.8 project I get the following error:

Error message:

.csproj file main project:

The Nuget package gets built and pushed to Nuget using DevOps pipelines.

This is the pipeline used for this package:

I have already tried solutions explained in this post: '' is not a valid version string." exception in nuget for VS2019

Does anyone have any idea what i'm doing wrong here? Thanks in advance!

Kind Regards,

Swedo