I finally found a solution that works by manually detecting the sidebar and then hiding it:
var sidepanel = crystalReportsViewer1.FindName("btnToggleSidePanel") as ToggleButton;
if (sidepanel != null) {
crystalReportsViewer1.ViewChange += (x, y) => sidepanel.IsChecked = false;
}
adding this namespace:
using System.Windows.Controls.Primitives;
The problem was that WPF ReportViewer is slightly different from Win Forms, some properties (such as ToolPanelView and ShowGroupTreeButton) were removed, I tried many different things, but above all, the only thing that did the trick.