Thanks a lot for your feedbacks ! I guess I found the solution I needed thanks to your clues.
With a SQL query, I have been able to fill a field called "hasApp" in my Data Extension. If it finds a raw in _PushAddress, then it puts a "1" in this boolean field :
S.SubscriberKey as IdSF,
1 as hasApp
FROM _PushAddress P
INNER JOIN _Subscribers S ON S.SubscriberID = P._ContactID
INNER JOIN CONTACTS_B2C C ON C.IdSF = S.SubscriberKey
I had to join _Subscribers to have a link between the ContactID and the ContactKey.
I'll run this query every day, then I'll be able to select all my contacts without a 1 in this field. However, this way tells me if someone already had once my app, not if he always has it. The best way would be to use the Status field.
But I'm not able to find a proper value for Status: it is always equals to 1 (optin) for all my devices while I have several devices optout (Contact Builder gives me a Status = Not Opted In, in the Membership tab)
Also, I'd be interetsed in the "Application Version" field we can see in the tab "Attributes", under MobilePush Data > MobilePush Demographics.
Can't find any answer on internet to have that !
Do you have some more clues for me ?
Thank you !