Hi Many Rains,
Thanks for your posting in Microsoft Community.
Currently, It's not feasible for the PowerPoint for Mac to compress the video as it doesn't conclude such an out of box feature like Office for Windows version.
Using the online video is a good idea here, but unfortunately your colleague can't open those videos. This could be caused by many different reasons, for instance: Her PowerPoint for Mac is in an older version which doesn't support online videos. Or her networks might behind some proxy settings which block all the links to the YouTube, etc.
So, in your current scenario, the only workaround is to export your embed videos and compress them via the 3rd party services. I've searched on the google, seems like there are many free online services which can help you reduce your video size.
But according to the code of conduct in this community, we couldn't provide you with such links, really sorry about it.
Also, I think it's a good idea for the PowerPoint for Mac to have the same function as Windows version does, so I would kindly suggest you share your feedback in the PowerPoint UserVoice, which is a specific platform for us to collect user's request. Your suggestion will help us improve our Products and give users a better experience.
We greatly appreciate your understanding.
Regards,
Alex Chen