Is VisualStudio MacOS using a different F# compiler than dotnet / Rider?

I'm trying to compile FsPickler on Mac.

The command line compilation works very well:

dotnet build -c Release

but when compiling the same project in Visual Studio (version 8.8), I start to get some compilation errors which have to do with the parsing of the files, which is really odd.

like this kind of errors:

the code it can't compile is this:

let currentLoadContext = lazy(
    match Type.GetType "System.Runtime.Loader.AssemblyLoadContext" with
    | null -> None
    | ty ->
        match ty.GetProperty "Assemblies" with
        | null -> None // property not available in netcoreapp < 3.0
        | assembliesProperty ->
            let loadContextM = ty.GetMethod("GetLoadContext", BindingFlags.Public ||| BindingFlags.Static, null, [|typeof<Assembly>|], null)
            let loadFromNameM = ty.GetMethod("LoadFromAssemblyName",  BindingFlags.Public ||| BindingFlags.Instance, null, [|typeof<AssemblyName>|], null)
            let asm = Assembly.GetExecutingAssembly()
            let currentLoadContext = loadContextM.Invoke(null, [|asm|])
            let getContextAssemblies () = assembliesProperty.GetValue(currentLoadContext) :?> seq<Assembly> |> Seq.toArray
            let loadFromAssemblyName (an : AssemblyName) = loadFromNameM.Invoke(currentLoadContext, [|an|]) :?> Assembly
            Some {| LoadContext = currentLoadContext ; GetCurrentAssemblies = getContextAssemblies ; LoadFromAssemblyName = loadFromAssemblyName |})

but it's not really relevant to the problem.

When I look at the details, I see that:

Target CoreCompile:
        /Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/fsharp/fsc.exe -o:obj/Debug/netstandard2.0/FsPickler.dll

and I'm now questioning: why do I even have Mono installed and what does Mono have to do with compiling the .net code with Visual Studio?

If I compile the same project with Rider, it works, with the command line, it works but with Visual Studio I get the errors above and a compiler coming from a Mono folder.

Can anyone shed some light as to why Mono is involved and if there are two versions of the compiler?