Using obs virtual camera as input, participants viewing in very low resolution

My first post here, as i cannot find a solution to that problem.
I’m using obs virtual camera as camera input in jitsi as i want to make a reletiv complex presentation to my students.
On my (linux) PC, i’m joining my room with firefox (as with chrome i had some camera problems).

It shows that i’m in HD mode, but no matter what i tried (changed resolution, in obs settings played with a lot o parameters i found i various forums and tutorials) the participants picture is usually LD (exactly ultra low, 300x150 or something like that!). Sometimes they receive HD or SD, but it does not remain so (changes back to LD)…
The same situation in a windows 10 Machine…

On the other hand, if i stream through zoom or webex (web version too), everything goes ok, the resolution is as expected.
Is there any idea about?