no hardware decoding on chromium-based browser

I have an intel uhd 630 graphic card working under Ubuntu 20.04. After a configuration of Firefox, it can use the hardware graphic decoding for H264 or VP9. But with chromium-based browser I can't enable hardware decoding : in chrome://gpu (or opera://gpu or even vivaldi://gpu) I got this error :

Accelerated video decode has been disabled, either via blocklist, about:flags or the command line.
Disabled Features: video_decode

I follow many tutorial, but I can't find the flag :

enable-accelerated-video-decode

Thanks in advance for your answers ?