Thanks Coin-coin
Finally I’m going to use that setting on Bunny iframe code :
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not selecting for responsive code

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On the default following code, replace size by width=“99%” height=“300”
<iframe src="https://iframe.mediadelivery.net/embed/3639/01bea422-9687-4058-9fcc-2b21dee6df2a?autoplay=false&preload=false" loading="lazy" width="1280" height="720" style="border: none;" allow="accelerometer; gyroscope; autoplay; encrypted-media; picture-in-picture;" allowfullscreen="true"></iframe>
The height will be a little too small on desktop, and a little too high on smartphone, but the width will be ok.
Onebox would be great, but as I can see we only have youtube, vimeo and TikTok for now on discourse.