Hi @Dlouie
There are some customizations that are possible for the Waiting Room, which can be found here in this support article, but unfortunately the customizations are limited. You would not be able to add much of a background, just a logo and some other info.
If you would like to submit any product feedback, I encourage you to visit our Zoom Feedback form, which is the official way to share any feedback or feature requests with the Zoom team. Thanks!