Hello everyone - there is a problem:
There are several Hikvision cameras on the local network (6 pcs).
There is an allocated IP address
I forward IP: port (to a specific camera) I connect normally, I log in, but the camera does not display the picture. From the local network, everything is fine.
What could be the problem?

The web page you get on connecting to it over the dstnat link includes code that tells your browser how to reach back to the camera for the actual video stream. You don’t say which Hikvision model you have, but your symptom tells me it likely includes a hardcoded IP under the assumption that you’re connecting from the same LAN.

Since IP cameras are famous for having poor security, relying on its login system to protect access to your camera is foolish to begin with. Set up a VPN instead of port-forwarding it out to the big bad Internet, solving both problems simultaneously.

Or use iVMS client for centralized management ?

I wonder, if 'depends' wearing mkx or krall will come in here and scold you for trying to fix an unsafe practice by an MT user, and trying to be nannies LOL.

Are you using browser to access camera ? or iVMS ?

In case you are using browser hikvision cameras are famous for not displaying picture on almost any browser except IE... I use edge with IE tab. Otherwise i have same symptom, log-in but no picture.

Also, as @holvoetn recommended, VPN or connect cameras to hik cloud and use iVMS. Are you recording video on SD card ?