Backup all Postman collection at once

As I see on another PC that I get the Export Data button, but that I was signed in, so I decide to sign in.
Usually I don’t do that beacause I don’t need it, and in the past I’ve done that and it made a mess between local and remote data.
Anyway, this time I really want to save my local collections so I signed in with an empty workspace in the cloud to avoid mixing data, as my reference is local.
Guess what, now I’m connected, I get the Export Data button, but all my collections are gone, and if I want to disconnect it say that I will lost any local data.
I lost many collections, nearly 1 Mo data.
Any idea ?