Here is an troubleshooting instruction for port forwarding, you can have a look:
http://www.tp-link.it/faq-785.html

Make sure the camera can be accessed internally via its IP plus port number first.
Some camera has a fixed port number to be opened. Pay attention to the port number.
And double check the internet/wan IP of the router is a public one.
IP addresses below are private IP addresses:
192.168.0.0 - 192.168.255.255 (65,536 IP addresses)
[*]172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses)
[*]10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses)

Hello
thanks for answer
I checked all items:
- camera is accessed on internal network at 192.168.2.89:1024
- https://www.yougetsignal.com/tools/open-ports/
provides me with the public IP address momentarily assigned: 2.194.21.24
- so that I can ping from outside network to it successfully
- checked port is correctly forwarded on router as specified in FAQ-785
- however I CANNOT access http://2.194.21.24:1024/ from the network
- and indeed https://www.yougetsignal.com/tools/open-ports/
finds that port 1024 on my IP 2.194.21.24 address is CLOSED

Again the question is:
DOES the Huawei USB dongle have an active role on stopping the traffic to the router?

Unfortunately I can't find at its local address 192.168.1.1 any way to set port forwarding or make a DMZ setting for the router at 192.168.2.1
However I thought USB dongles should not affect traffic to the router

thanks a lot for help

DMZ IP address should be the IP address of your camera, 192.168.2.89.
The dongle is the internet source for the router. It does affect the traffic.
Can you ping 2.194.21.24? it seems this IP address is blocked.
Is this IP address showing under 3G/4G or Internet part on the router's web management page or provided by your iSP directly?

YES: DMZ IP address is the IP address of camera, 192.168.2.89
YES: the dongle address: now 2.194.4.193 is pingable from outside world:
Risposta da 2.194.4.193: byte=32 durata=283ms TTL=52
and it is the public IP address of the SIM Modem Huawei E3131, as the screenshot shows:

However I read something more on coupling Huawei 3G USB dongles and routers and I understood there might be something else not working on transferring traffik from the dongle to the router due to the default setting of the dongle which is interfaced by a software "Hilink" rather than as a simple modem as it used to be in the past, pls see:
https://zedt.eu/tech/hardware/switch-huawei-e3131-hilink-modem-mode/

so that it should be necessary to switch the modem from Hilink to modem mode

Unfortunately I have also read some contrarian experience so that this action cannot revert the 3G dongle to the original mode eventually loosing its functionality.

I wonder anybody has any experience on that and could help
thanks

correct link is for suggestion to switch the 3G dongle to modem mode from Hilink:
https://zedt.eu/tech/hardware/switch-huawei-e3131-hilink-modem-mode/

I saw it was cut

The 2.194.4.193 is the IP address of the dongle but the dongle will provide another IP address to the router.
If the IP address provided to the router is not a public one, then port forwarding can't work.
As you mentioned, change the dongle to modem mode may help.

tried several methods to disable Hilink, did not succeed:

https://zedt.eu/tech/hardware/switch-huawei-e3131-hilink-modem-mode/
because the COM ports are not shown on the device list

and others are not effective for reasons cited in the link

No way, hopeless adventure

How about contacting the sim card provider for help?

the SIM provider does not know about the modem one is using and they already helped providing immediately a public IP address for the SIM

On the other hand I tried to contact Huawei support both by email and with FB messaging: so far no answer

What about if I switch to 3G modem/router like the Huawei E5756?
I would like to make sure that I can do port forwarding and dyndns
but I CANNOT find the manual on the internet

I wonder there is a more reliable 3G modem maker other than Huawei

thanks anyway