The /online part of the DISM command relies on Windows Update Service to work properly. If this is part of what's broken, DISM might fail.

Instead, use a new download of the Windows image from Microsoft to process the repair.

If you're not sure how to get a Windows .iso (image) file, use the USB Boot Drive Creation Guide, but on Step 6, select .iso and choose a location to save it.

Although this Guide is for Windows 10, it is also relevant for 8 and 11.