This is not permissible. One should only make the prescribed dhikr taught to us by the Prophet salla Allahu aliaihi wa sallam.

Is it okay to make up ones own phrases of praising and remembering Allah by mentioning His names and attributes like for example saying “Allahu adheem, Allahu kareem, Allahu raheem, etc.” same as how one says Allahu akbar and so on, as long as one does not do it regurlaly or daily and at specific times?