Opera's autoplay policy may mute background MP4 videos. Try adding user interaction elements to play sound or check your video tag for a "muted" attribute. If that doesn't work, consider re-encoding the video file.
@nuzz-y Same issue, tried re-applying the wallpaper i used to have from the Opera Addons store. When I click "add to Opera", it just prompts a download of a .avzip file. I like the chat and media player integrations, but download and add-on management for Opera GX are just So Buggy!
@quik Yes my system can handle it because when the animated background is loaded i can re-open a new tab and it doesn't freeze, but if i stay on the same tab for a while, when i open a new tab i have the problem again! I think they should preload the animated background at the start of OperaGX instead of at the opening of the tab! And i'll try next days without the animated background and comeback here to say if the problem persists!