<ui:ContentDialog x:Class=".View.Dialog.XXXDialog"
                  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                  xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
                  xmlns:ui="http://schemas.modernwpf.com/2019"
                  mc:Ignorable="d" >
    
</ui:ContentDialog>

public partial class XXXDialog : ContentDialog
{
    public XXXDialog()
    {
            InitializeComponent();

            PrimaryButtonClick += (_, _) =>
            {
                // Condition here cause "Enter" key will cross this
                if (IsPrimaryButtonEnabled)
                {
                    ;
                }
            };

            Closing += (_, args) =>
            {
                // If the PrimaryButton is disabled, block the "Enter" key
                if (args.Result == ContentDialogResult.Primary && !IsPrimaryButtonEnabled)
                {
                    args.Cancel = true;
                }
            };
    }
}

一个魔法
IsPrimaryButtonEnabled="{Binding ElementName=ApiKey, Path=Text.Length}"

一些基础属性
CloseButtonText="Close"
PrimaryButtonText="Save"
DefaultButton="Primary"

注意ContentDialog需要考虑键盘按键 ESC Enter 键的穿越性，需结合IsPrimaryButtonEnabled状态