There are two different “Sonoff Zigbee 3.0 USB Dongle Plus” models; the model “ZBDongle-P”) based on Texas Instruments CC2652P and the model “ZBDongle-E” based on Silicon Labs EFR32MG21.
If you bought “ZBDongle-E” then should specify in Z2M configuration that you have a “ezsp” adapter:
https://www.zigbee2mqtt.io/guide/configuration/adapter-settings.html
Optional: adapter type, not needed unless you are experiencing problems (default: shown below, options: zstack, deconz, ezsp)
Also, preferably use “serial/by-id” device path instead as “/dev/ttyACM0” can change on reboot.
While most devices need at the very least the serial device path, like “/dev/ttyUSB0”, it is still recommended to use device path from “/dev/serial/by-id” folder, e.g., “/dev/serial/by-id/usb-Silicon_Labs_HubZ_Smart_Home_Controller_C0F003D3-if01-port0” (FYI, a list of available device paths can be found in {% my hardware title=“Settings > System > Hardware” %} > dot menu > **All Hardware).
Example ("adapter: ezsp:" and “serial/by-id”, note example ID may not be exactly same for you):
serial:
port: /dev/serial/by-id/usb-Silicon_Labs_Sonoff_Zigbee_3.0_USB_Dongle_Plus_0001-if00-port0
adapter: ezsp
PS: Better to post Zigbee2MQTT issues to → https://github.com/Koenkk/zigbee2mqtt/discussions