Without much ado, here is a Python script that will allow you to dump password from the Gnome password manager (also known as Seahorse, and used in other desktop environments such as Cinnamon) into a JSON file.
This is useful for just viewing all your stored passwords (which are not always visible in the password manager GUI), but it will also import them again, which is especially useful when you want to pull in all your saved passwords from an old machine.
Please see the top of the script for instructions. You'll need to know how to install Python and related packages - this is not a point-and-click solution, sorry!