When opening a XAML file in Visual Studio, the designer can take a long time to load, even when you don't actually need it. To avoid this delay, you can change a Visual Studio setting to open XAML files in full XAML view by default, skipping the designer entirely. You can still open the designer manually whenever needed. The option is located at Options/Text Editor/XAML/Miscellaneous/Always open documents in full XAML view.
XAML Options in Visual Studio
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