Difficulties reading/writing camera and smartphone memory

Hello, I posted this support request about four weeks ago in the forum but haven't received any help yet. It has become crucial for me to communicate with my smartphone so this is important. Thanks in advance!

I've got difficulties reading and writing files on my camery and my smartphone connected with USB.

The camera is a Panasonic Lumix with SD card. Of course I could take the card out but I'd like to use USB sometimes. I can read and copy but I can't delete any pictures. I haven't found any settings in the camera menu to change that.

The smartphone is a WIM Lite with Android 7.1.1. Choosing 'Transfer of pictures' in the Smartphone menu, I'm able to read and write pictures. But I'm not able to access the 'music' folder while choosing 'File transfer'. Also here, I didn't find any option to change that in the settings.

Does anybody have an idea? Is it a problem of proprietary drivers or software? Or is it a more general incompatibility?

Thank you in advance

anatom