link connected then nothing more normally means that the interface is up but there is no configuration, maybe the interface is not running a dhcp client, maybe NetworkManager’s connection config has become corrupt or rendered unreadable for some other reason.
ifconfig is not a good choice of tool/utility for networks managed by NetworkManager. nmcli is the tool that should be used, to get some basic information on state…
nmcli dev
Will list devices and their basic state, while…
nmcli conn show
will list connections and their basic general state, while…
nmcli conn show <connecion-name>
will show the configuration of the named connection in detail.
ip can also be used to determine assigned/configured IP addresses and routing etc.
From your recent thread on tethering with MacOS…
Did this setting/configuration persist? By default NetworkManger handles config/setup of all network devices/interfaces, however, if the interface has been configured elsewhere outside of NetworkManager, NetwrokManger won’t takeover. I suspect that your use of ifconfig may have caused NetworkManager to ignore the usb0 interface.
Using ifconfig to configure the IP address or any other parameter of an interface handled by NetwrokManager is a bad idea and is likely to introduce problems.