Thanks @ThinhDinh @Nocodemobileapp @kyleheney.
Maybe should I put all my flow* (1 to 4) in 1 single screen / tab, which would be a “User” sheet in a Form.
Screen 1. Access without account/email -> Upload document [user specific column] -> Copy [button action]
Screen 2. Choose options [user specific column]
Screen 3. Enter user’s email & adress [create user profile]
Screen 4. Send email [button send] to the user with the previously collected information (when the user was not signed-up)
[Edit: apparently forms cannot write to user specific columns… arrgh 🆕 New containing screen context for conditions]