Update It's working actually, I had to adjust my local IP address, which is constantly changing. So sorry for the inconvenience.
I can ssh to my computer1 from my computer2 on my local network, using my local IP:
However, I want to ssh from outside my home, using my public IP:
I have access to my router (ZTE F600W) configuration but obviously can’t make port forwarding right.
I tried different things and reboot the router like 10 times already.
The firewall on my computer is disabled. Is there something else I can possibly check?
As suggested by @Enrico Polesel, I stabilized my local IP on my computer manually, instead of getting one automatically via DHCP.
It seems to work so far.
Now the last improvement I can make is using a dynamic IP service because my public IP is dynamic.
I'm using the service "my.noip.com" and it works fine.
Now I can ssh to my computer with the same hostname, and everything is handled correctly to my computer :-)