Hi @NE NZANZA ,
Try to add code below in your csproj file one by one and test the project.
<ItemGroup>
<FrameworkReference Include="Microsoft.AspNetCore.App" />
</ItemGroup>
and
<ItemGroup>
<ProjectCapability Include="SupportsSystemWeb" />
</ItemGroup>
Try to rebuild the project and see whether it makes any diffrence.
If the issue persists, try to run dotnet restore or dotnet restore --force-evaluate command.
Please do let me know your test results.
Note: Please take the backup of your project and then try to test the suggestions above.
Best Regards,
Deepak