Hi 123qwert123,
Some routers block P2P connections of 2 devices from different networks without using DMZ or port forwarding. Since Remotly currently uses a random free port for P2P connections it is not possible to open a single port on the router to make the P2P connection work. Currently it is required to add the IP of the device to DMZ on the router.
In PC version 1.9.6 (Android 1.20) we will add a fixed port that will be tried first. If it fails it will try the default port returned by the operating system. This port will be fixed to 42015.
In PC version 1.9.7 (Android 1.21) we will add the possibility to select your own port to use for P2P connections. You will be able to use a port that is not used by anyone else on your device.
This way you will only need to port forward one port and not use the DMZ (which is not very safe).
Please note that when connecting via mobile networks (LTE/5G) you will not be able to change their port forwarding configuration and will always need to use Connect Anywhere. This is why we will soon give you the possibility to setup your own Connect Anywhere server in your local network on a Raspberry Pi (or similar) device. This device will then be used for Connect Anywhere connections and you will have the same lag as using P2P

And it will always work (without any difficult router setup changes).
Hope this clarifies.