I want to change the content type of a folder in a sharepoint site using GraphServiceClient. The goal behind this, is to attach custom columns to the folder and store values in those columns.

I access the folder like this:

var fo = await GraphClient.Drives[id].Items[_folderId].GetAsync(
    c => c.QueryParameters.Expand = new[] { "ListItem" }
    );

I’ve read that the ContentType can only be applied to the corresponding ListItem. So I access it like this:

var foli = fo.ListItem;

Now, I check the ContentType

if (foli.ContentType.Name == "Ordner") // "Ordner" is German for Folder
{
    //loop through available ContentTypes
    var ct = await GraphClient.Sites[id].ContentTypes.GetAsync();

    foreach (var item in ct.Value)
    {
        //find id of new ContentType
        if (item.Name == "newContentType")
        {
            var c = item;

          //What do I need to write here?
          foli.ContentType = c; // does not work, because ContentTypeInfo is needed instead of ContentType
        }
    }

}