Ok folks, because I am stubborn, I tried something, and IT WORKS !!!
In the app, I selected Generic, then BUS Urmett (the last one in the list), and followed the instructions. It was the only one which showed me cables with L1 and L2 (what I mentioned above).
I tried it and… my building’s door opened! Houraaaaa.
So I can tell that Intercom Comelit Okay 2408W/A is fully compatible with Opener !!!