Don't think about it, it's not in use anymore.
But if you want to know:
Long long ago, before Covid was a thing,
Disneyland Paris was experimenting with how to regulate character meetings better.
They made use of an app called Lineberty. It was only in use at the Studios for a handful of scheduled meet & greets. Impromptu meet & greets didn't have this.
It was an app where you could book a ticket to see a character.
At park opening, you open the app, you select the character, you select the amount of people and you got a ticket. Or not. These tickets went fast when it was for Frozen characters.
The thing is: You didn't get a fixed return time. It was not a fastpass where it said 'return between 10 and 10:30. The app tracks how quickly the meets go, if people show up or not.
So when you book it might say 'return 2 hours from now', but if people didn't show up or it goes quicker than average, it could be reduced.
When it's 10 minutes before your time, you get a push message from your app and you're time is getting closer and you can start making your way to the character. The cast member checks your reservation on an ipad and you get in line. And within 5 - 10 minutes you meet the character.
There was a 15 minute grace period. So if you were at a restaurant or on a ride, you didn't have to jump up and run to the character.
I don't know exactly why they stopped it, covid stopped it temporarily for sure, but my best guess is you had to be in the know for this. Most popular meets sold out within seconds and therefore all other guests were disappointed.