You can resize the SfExpander Content based on the content size by using DynamicSizeMode as Content in Xamarin.Forms.
You can also refer the following article.
https://www.syncfusion.com/kb/11431/how-to-autofit-the-expander-content-in-xamarin-forms-sfexpander
XAML
Added Editor control to Expander content and set DynamicSizeMode to Content. To change the content size based on the text, set AutoSize as TextChanges for Editor control.
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:ExpanderXamarin"
xmlns:syncfusion="clr-namespace:Syncfusion.XForms.Expander;assembly=Syncfusion.Expander.XForms"
x:Class="ExpanderXamarin.MainPage">
<ContentPage.Content>
<ScrollView BackgroundColor="#EDF2F5">
<StackLayout>
<syncfusion:SfExpander DynamicSizeMode="Content" IsExpanded="True">
<syncfusion:SfExpander.Header>
<Grid HeightRequest="50">
<Label Text="Veggie burger" VerticalTextAlignment="Center"/>
</Grid>
</syncfusion:SfExpander.Header>
<syncfusion:SfExpander.Content>
<Grid>
<Editor AutoSize="TextChanges" Text="Veggie burger, garden burger, or tofu burger uses a meat analogue, a meat substitute such as tofu, textured vegetable protein, seitan (wheat gluten), Quorn, beans, grains or an assortment of vegetables, which are ground up and formed into patties."/>
</Grid>
</syncfusion:SfExpander.Content>
</syncfusion:SfExpander>
</StackLayout>
</ScrollView>
</ContentPage.Content>
</ContentPage>
Output