No video playback for me either - with or without extensions.
Youtube, Whatsapp, Amazon product videos - the list goes on!
This issue has been going on for quite some time now, which is a surprise. Because of this I am having to use different browsers; where video playback does work - but this is a shame as I prefer Opera 
Version:69.0.3686.77
Opera is up to date
Update stream:Stable
System:Linux Mint 20 (x86_64; X-Cinnamon)