HI ISIN,
if you are applying for REST, permitted activities are studying a full-time study program at a university and a part-time employment.
For more information, please have a **** at this website: https://***.bamf.de/SharedDocs/Anlagen/EN/MigrationAufenthalt/flyer-rest-mobilitaetsrechte.pdf;jsessionid=8E28322763B4F5B918262E081854CC2B.intranet231?__blob=publicationFile&v=7
Hope this helps a bit.
Best wishes,
Anita