Hello Timo Pape,
Good day! Thank you for posting in Microsoft Community. I will be happy to assist you with this request.
Based on your description I understand that you can't download O365 Apps on macOS, Please correct me if I am wrong. Thank you.
I have done some research and I observed that the issue you're facing is happening with MAC OS BigSur 11 version which became out of support and you can't use O365 Apps On, So it's recommended to install the machine's latest macOS, so that you can use O365 Apps and keep receiving updates.
You can follow the below steps for updating your macOS:
- From the Apple menu in the corner of your screen, choose System Settings. Click General in the sidebar, then click Software Update on the right.
- Or in earlier versions of macOS, choose Apple menu > System Preferences, then click Software Update.
- If Software Update finds new software, click the Update or Upgrade button to download and install it. You will be asked to enter your administrator password, which is the password you use to log in to your Mac.
You can check more: Upgrade macOS to continue receiving Microsoft 365 and ...
Incase you don't need to upgrade your OS, you can install Office 2019 as it's compatible with macOS Big Sur 11.7.10
Please let me know if you need further assistance, Thank you.
Best regards,
Stacey
