So I got it working by buying an Terra MT47 modulator !

thanks to @mayasynth@eldritch.cafe and her advices !

seems that proxmox requires a complete install which is impossible in my cas though

So what is happening is quite simple:

I AM FRENCH

which is considered bad when using old TVs. Why ?

Because we use L and L’ bandes when most modulator are using B/G or things like that
So, that won’t work properly.