Connect with a new wireless?

I'm in a neighbor's apartment with my laptop, but I can't connect to their Wi-Fi. It loads forever and then after 2 minutes it says that the connection has failed and that before I was even asked for a password. What can I do there?
I'm talking about the Wi-Fi of my girlfriend before you think otherwise here

There may be something in the router who knows what.

My first thought was: Mac filtering (I have also activated for security reasons).

This means that only devices will get access to the router / Internet whose MAC address is stored in the router as an approved device. Each device has its own, unmistakable Mac address. This must be entered in the router.

There are of course other possibilities, but this can be said from the distance bad…