AFAIK, short of updating code and compiling your own version of Jitsi Meet, the only way to influence the list of virtual backgrounds is to specify virtualBackgrounds list in the return payload of dynamicBrandingUrl.
You can remove the virtual background option completely by overriding toolbarButtons and leaving out the select-background option. This however also means users cannot use background blur.
You can try out how that would look by going here and deselect “Select Background” from the toolbar buttons.
Btw, the fact that dynamicBrandingUrl is the only option should not be an issue if you are self-hosting. There’s no reason why the URL cannot reference a local resource, so you don’t need the hassle of hosting the JSON elsewhere.
For example, create a file like this in /usr/share/jitsi-meet/static/branding.json:
The problem is i have different types of users and want to load a diferent series of images for each user so i can overwrite the config depending on external info.