It seems that height adjustment cannot be made automatically because you set "
HeightRequest=50". You can easily resolve the problem with deleting HeightRequest=50 from your button.
It is better to use Grid to adjust the height according to the screensize.
Example:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="80*" />
<RowDefinition Height="20*" />
</Grid.RowDefinitions>
<Grid Grid.Row="0">
</Grid>
<Button Grid.Row="1" BackgroundColor="{StaticResource color1gray}"
BorderRadius="5"
VerticalOptions="Center"
HorizontalOptions="Center"
Text="Cancelar" />
</Grid>
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