You could try to define the MenuItemTemplate
as a workaround to achieve this:
<MenuItem Text="Logout" IconImageSource="logout"
Command="{Binding SignOutCommand}">
<Shell.MenuItemTemplate>
<DataTemplate>
<Grid >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0.2*" />
<ColumnDefinition Width="0.8*" />
</Grid.ColumnDefinitions>
<Image Source="{Binding Icon}"
Margin="0,300,0,0" //You need to adjust the margin value yourself
HeightRequest="30" />
<Label Grid.Column="1"
Margin="0,300,0,0" //You need to adjust the margin value yourself
Text="{Binding Text}"
FontAttributes="Italic"
VerticalTextAlignment="Center" />
</Grid>
</DataTemplate>
</Shell.MenuItemTemplate>
</MenuItem>