This is exactly what I was looking for recently, and sadly I couldn’t find one either.
However, you can integrate your own widgets into Qt Designer by creating a custom widget plugin. Qt Creator even provides a boilerplate project template for this in C++ (I’m not sure yet on the PySide process), so it’s pretty easy to get started. Once built, your plugin will appear in Designer just like the default widgets.
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I recently built one myself in C++ for another project using Fluent UI–style widgets. The repo’s here if you’d like to take a look: https://github.com/alviansm/QtFluentWidgetPlugin.
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