Soylent should be fine to use in composting as with other food waste or organic materials. How and what you choose to compost is a matter of personal choice.
Soylent is plant-based which means it does not contain any meat, eggs, or dairy in any of the formulas. This is helpful for composting, as many composters recommend steering away from these foods due to potential risk of odors or attracting pests.
We love this idea for recycling your unused Soylent. Thanks for helping us to be more sustainable!