This is best done using OBS Studio with the NDI plugin.
If the background image needs to be seen without your webcam or with picture in picture where your webcam image is in a corner then OBS can manage this and even key a separate background behind you when doing a PIP. You can resize and relocate the webcam image on the screen. If you output OBS to a second screen then you can get higher resolution by using screen share. If you don't have a second screen you can output from OBS as NDI as a webcam and use advanced sharing "second camera" to send the OBS output as 720P instead of the normal 360P that Zoom's virtual backgrounds go out as to your participants.
There are numerous youtube videos explaining how to use OBS Studio. Or you can send me a private message to get personal training.
If this works please click accept as a solution.