I am really suprised that the answer is nowhere to find. I can see that I can migrate applications like here: https://www.qnap.com/en/how-to/faq/article/how-to-migrate-app-center-apps-to-another-nas-volume
However I cannot force the Apps to be installed on the specific volume I created just for applications. Always picks the other one I used for Active Backups of the clouds storages.
I would appreciate any help in finding that.