Safari - Rise: no audio in storyline blocks

Hallo everybody. Hope someone can help me in fixing this problem.

Yesterday I updated Safari to 15.0 version. Since then I get no audio in Storyline blocks (interactivity with audio) inside my Rise projects (yesterday everything was working, though). I imported all the blocks anew, after fixing all the Safari preferences, but nothing changed. Everything is  working properly in Firefox and in GoogleChrome (and in Safari 14). How can I get my audio back?

Thanks a lot for your help.

Daniela