@IvaK_net: The use case is as follows. I have standard PSDs with smart objects for various screen sizes.
I want to show various screens on the same template. Currently, I take the screenshot and replace the images one by one.
Ideally, I would like to issue a command from my terminal to use the screenshots (which I generate from another tool) in a folder and pop them into the smartobject and export the output to an output folder.
I am still not sure if I understand what you need.
If you have a Smart Object, which occurs multiple times in your PSD, you can double-click it, put all your screenshots inside it and save it. Then you can simply switch the visibility of layers inside a smart object.
Using Photopea would require running it in a browser window, it would be hard to connect it with your terminal.
Do you need to edit your own PSDs, or you want it to be done automatically in your app?