I can't change the main application form.

[jeanssp]

<ContentPage
x:Class="Maui11082023.Mvvm.View.AccountsPage"

xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         
xmlns:model="clr-namespace:Maui11082023.Mvvm.Models"
xmlns:viewmodel="clr-namespace:Maui11082023.Mvvm.ViewModel"
xmlns:ios="clr-namespace:Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific;assembly=Microsoft.Maui.Controls"
ios:Page.UseSafeArea="True"
Title="Счета"
x:DataType="viewmodel:AcctViewModel">
<Grid
    ColumnDefinitions="*,*"
    ColumnSpacing="5"
    RowDefinitions="*,Auto"
    RowSpacing="0"
    BackgroundColor="{AppThemeBinding Light={StaticResource LightBackground}, Dark={StaticResource DarkBackground}}">
    <RefreshView
        Grid.ColumnSpan="2"
        
        Command="{Binding GetAcctsCommand}"
        
        IsRefreshing="{Binding IsRefreshing}">
        <ContentView>
            <CollectionView
                    ItemsSource="{Binding Accts}"
                    SelectionMode="None">
                <CollectionView.EmptyView>
                    <StackLayout Padding="100">
                        <Image
                                HorizontalOptions="Center"
                                HeightRequest="160"
                                WidthRequest="160"
                                Source="nodata.png"
                                VerticalOptions="Center" />
                    </StackLayout>
                </CollectionView.EmptyView>
                <!--<CollectionView.ItemsLayout>
                        <GridItemsLayout  Orientation="Horizontal" Span="3"/>
                    </CollectionView.ItemsLayout>-->
                <CollectionView.ItemTemplate>
                    <DataTemplate x:DataType="model:AcctDto">
                        <Grid Padding="10" HorizontalOptions="Fill">
                            <Frame HeightRequest="125" Style="{StaticResource CardView}">
                                <Frame.GestureRecognizers>
                                    <TapGestureRecognizer 
                                            Command="{Binding Source={RelativeSource AncestorType={x:Type viewmodel:AcctViewModel}}, Path=GoToDetailsCommand}"
                                            CommandParameter="{Binding .}"/>
                                </Frame.GestureRecognizers>
                                <Grid Padding="0" ColumnDefinitions="125,*">
                                    <Image
                                            Aspect="AspectFill"
                                            HeightRequest="125"
                                            Source="{Binding AcctName}"
                                            WidthRequest="125" />
                                    <VerticalStackLayout
                                            VerticalOptions="Center"
                                            Grid.Column="1"
                                            Padding="10">
                                        <Label Style="{StaticResource LargeLabel}" Text="{Binding  DebetSaldo}" />
                                        <Label Style="{StaticResource MediumLabel}" Text="{Binding CreditSaldo}" />
                                    </VerticalStackLayout>
                                </Grid>
                            </Frame>
                        </Grid>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>
        </ContentView>
    </RefreshView>

    <Button
        Grid.Row="1"
        Grid.Column="0"
        Margin="8"
        Command="{Binding GetAcctsCommand}"
        IsEnabled="{Binding IsNotBusy}"
        Style="{StaticResource ButtonOutline}"
        Text="Get Monkeys" />


    <ActivityIndicator
        Grid.RowSpan="2"
        Grid.ColumnSpan="2"
        HorizontalOptions="Fill"
        IsRunning="{Binding IsBusy}"
        IsVisible="{Binding IsBusy}"
        Color="{StaticResource Primary}"
        VerticalOptions="Center" />
</Grid>

[davidortinau]

Definitely odd. Did you figure it out?

To troubleshoot this I would usually start adding bright colors to the background of the layout elements all the way to the ContentPage, and see how things are actually sizing.

I don't think you need that ContentView wrapping the CollectionView fwiw.