You can see the known good configuration here: Port forwarding on Quectel EG912Y-EU - #6 by jfrog
This example is applicable to your modem as well.
If the problem persists, show the output of AT+CGPADDR, AT+CGDCONT? and AT+QICSGP=1 (assuming context 1 is in use).
Then on the Linux host collect the output of
ip a
ip r
ip l