I think that what you are seeing means that adb cannot detect that a phone is connected. To check type ‘adb devices’. If it gives you no result, then either 1: your phone is not connected properly 2: you have not enabled USB debugging on your phone or 3: you don’t have the correct driver installed (assuming you are working on Windows).
If it is 3: then I don’t know how you should proceed: I haven’t used Windows in many years. DOyou have Xperia Companion installed on your PC https://www.sony.co.uk/electronics/support/mobile-phones-tablets-mobile-phones/xperia-z3-compact/articles/00236877?. If not, then install it and check your device is detected.