SunnyPz:
Any attempt to go to the device manager gets me to the page where new devices are added, not the page where devices are listed.
It should be Arduino Manager for Linux.
Do you mean the page that has "Add new board", "Add new device", "Add new SIM"?:
If you're on that page and you don't see any devices listed, it just means you don't have any devices and you need to add some.