You can’t.
The visible property seems to be voluntarily removed from the property editor of Qt Designer and you can’t add it back.
You can add the property manually to the .ui file by adding the following XML block inside the node for the widget you want to hide:
<property name="visible">
<bool>false</bool>
</property>
But the widget won’t be visible or movable when you reopen the interface with the designer. It will still appear in the widget hierarchy though.