@Cher Hi, looking at your screenshot, I think there is a bug in the modem firmware. If you look at the logs on the right you can see:
+CPIN: RE DY
This means the sim card is detected and ready. However, one letter is missing. This is supposed to be +CPIN READY. So I think the serial tool is therefore failing to interpet the correct string.
Can you query the CCID/IMSI? If it returns a number then the sim card is for sure working. You can also try updating the firmware
For Quectel BG96 you can verify the network connection with the following AT commands
AT+CGPADDR //check IP address
AT+CGATT? //check if attached to network
AT+COPS? //check current set MNO
AT+COPS=? //scan network for mobile operators
AT+CGDCONT? //check APN
AT+QPING=1,"172.27.131.100" //ping UDP server