Hey there qazwsxedcrfvtgbyhnujmikolpñ,
Thanks for reaching out to Apple Support Communities. I understand you’re having issues playing videos in Safari after updating macOS. I’ll be happy to help.
I’ve updated and am using macOS Catalina and not having any issues playing videos in Safari. Is this happening in multiple websites? If it is, quit Safari, restart your Mac, and see if this happens in a new user account to isolate the issue:
How to turn your Mac on or off
How to test an issue in another user account on your Mac
Make sure you don’t have any extensions or plug-ins active that could cause this issue as well. Take a look at these links to help with this:
Using Internet plug-ins in Safari for Mac
Install and manage Safari extensions on your Mac
If you continue to have the issue after that, you can reach out to Apple Support using the following link to continue to look into this with you:
Contact Apple Support
Cheers