I'm really struggling for a few days to connect a SonOFF temperature sensor with Node-Red without any luck.
I installed zigbee2mqtt to Raspberry Pi accordingly to this website: Linux | Zigbee2MQTT
After configuring the configuration.yaml file and starting the service with commands cd /opt/zigbee2mqtt and npm start I started to see in Raspberry Pi console information sent by the Temperature sensor:
Going to Node-Red interface I installed several modules and after many trials I found one that might try to connect called node-red-contrib-sonoff-tasmota : Sonoff device
After doing all these steps, the status of the SONOFF block remains on "Connecting"
Could you please let me know if there is any solution to display the temperature values in Node-Red?
This is your issue. When using Zigbee2MQTT, you need to use MQTT not another node that connects direct to the SONOFF (or via the Tuya cloud).
Here is an example set of MQTT topics from my own config:
Each device defined to zigbee2mqtt should have its own unique topic. You need to add an MQTT-in node to your flow instead of the sonoff node. Set the mqtt node to listen for the specific topic.