Я не использовал библиотеку, но ShareOptions.cs
кажется довольно хорошо задокументированным: https://github.com/jguertl/SharePlugin/blob/master/Share/Share.Plugin.Abstractions/ShareOptions.cs
/// <summary>
/// Platform specific Share Options
/// </summary>
public class ShareOptions
{
/// <summary>
/// Android: Gets or sets the title of the app chooser popup.
/// If null (default) the system default title is used.
/// </summary>
public string ChooserTitle { get; set; } = null;
/// <summary>
/// Tizen: Excluded App Types
/// </summary>
public ShareAppControlType ExcludedAppControlTypes { get; set; } = 0;
/// <summary>
/// iOS: Gets or sets the UIActivityTypes that should not be displayed.
/// If null (default) the value of <see cref="Plugin.Share.ShareImplementation.ExcludedUIActivityTypes"/> is used.
/// </summary>
public ShareUIActivityType[] ExcludedUIActivityTypes { get; set; } = null;
/// <summary>
/// iOS only: Gets or sets the popover anchor rectangle.
/// If null (default) the option is not used.
/// </summary>
public ShareRectangle PopoverAnchorRectangle { get; set; } = null;
}