Hi @Fabian ,
How can I specify/force to be "clients" my default address book for newly created contacts?
I am afraid this is not feasible. Based on my test and research, currently the default contact folder cannot be changed in Outlook for mobile, and the newly created contacts can only be saved in "Contacts". In this case, you can use the outlook desktop to move the contact to your preferred folder.
I’ve tried submitted this feature request via the in-app “Suggest a Feature” option in my Outlook for android. You can also make a suggestion via In-app help : Go to Settings > Help & Feedback > Suggest a Feature.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.