iCloud Photo - no video sound
I have an iCloud+ 400GB subscription. On my iMac, in the Photos app settings, I have iCloud Photos check-marked. So, my entire Photo library is uploaded to iCloud.
So far so good. This part works. Folders and subfolders and Poster frames of videos are also all there.
However, all videos in iCloud Photos have no sound. But all of them have sound in the Photo app on my iMac. And the sound in my Browser (Safari) is also working fine.
When I open a video in iCloud Photos I can see that the audio setting is on and set to 100. See screenshot 1. But another setting at the top of the video window seems to indicate that the sound is off. See screenshot 2.
How do I get sound for my Videos?
iMac 27″, macOS 10.15