I can't count the number of times I've seen folks post on snake groups asking for recommendations for snakes that don't eat rats and mice. It's a serious drawback to what is otherwise an excellent pet. Even snakes that happily eat a diverse diet of fish and insects (garter snakes, for example) still need the occasional mouse in order to not develop a nutritional deficiency.
There is one breed of pet snake that does eat an entirely vegetarian diet, and it is called the Dasypeltis sp., or African Egg-Eating snake. They're beautiful snakes, but sourcing their diet is very challenging. They require very small eggs as their entire diet.
The eggs I buy are infertile finch eggs, from an independent finch breeder. In the 8 months since I've owned my egg-eater, she's had to raise her prices as well as introduce a waiting list due to the breed becoming more popular.
Figuring out a way to make synthetic finch and button quail eggs with inert, reptile-safe shells would cause this breed to seriously take off, and probably supplant many adoptions of other varieties of snakes.
To whoever was commenting below about reptile pellets, they do exist, but currently they are more expensive than feeder mice/rats, and they're still made of smaller animals. https://reptilinks.com/