I noticed in the IOS .csproj, some lib targeted netstandard2.1 instead of 2.0:
<Reference Include="Microsoft.AspNetCore.Connections.Abstractions, Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Connections.Abstractions.6.0.1\lib\netstandard2.1\Microsoft.AspNetCore.Connections.Abstractions.dll</HintPath>
</Reference>
<Reference Include="Microsoft.AspNetCore.Http.Connections.Client, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Http.Connections.Client.6.0.1\lib\netstandard2.1\Microsoft.AspNetCore.Http.Connections.Client.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.Http.Connections.Common, Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Http.Connections.Common.6.0.1\lib\netstandard2.1\Microsoft.AspNetCore.Http.Connections.Common.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.SignalR.Client, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.SignalR.Client.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.SignalR.Client.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.SignalR.Client.Core, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.SignalR.Client.Core.6.0.1\lib\netstandard2.1\Microsoft.AspNetCore.SignalR.Client.Core.dll</HintPath>
<Private>True</Private>
</Reference>
Switching back to netstandard2.0 worked for me. (My Common library is a netstandard2.0)
<Reference Include="Microsoft.AspNetCore.Connections.Abstractions, Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Connections.Abstractions.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.Connections.Abstractions.dll</HintPath>
</Reference>
<Reference Include="Microsoft.AspNetCore.Http.Connections.Client, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Http.Connections.Client.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.Http.Connections.Client.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.Http.Connections.Common, Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.Http.Connections.Common.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.Http.Connections.Common.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.SignalR.Client, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.SignalR.Client.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.SignalR.Client.dll</HintPath>
<Private>True</Private>
</Reference>
<Reference Include="Microsoft.AspNetCore.SignalR.Client.Core, Version=6.0.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60, processorArchitecture=MSIL">
<HintPath>..\..\packages\Microsoft.AspNetCore.SignalR.Client.Core.6.0.1\lib\netstandard2.0\Microsoft.AspNetCore.SignalR.Client.Core.dll</HintPath>
<Private>True</Private>
</Reference>