SurrealDB [1] is a fairly complete database written in Rust. I've used it for fairly small web apps and it felt comfortable to work with coming from MongoDB.
[1] https://github.com/surrealdb/surrealdb?tab=readme-ov-file
[1] https://github.com/surrealdb/surrealdb?tab=readme-ov-file
Either you need to make it easy and zero friction to adopt like duckDB and let people find out themselves in an hour or two or you need to provide some sort of benchmarks + evidence that it isn't going to die on its arse the moment you put larger than memory amounts of data in.
Nearly all of these projects work fine for in memory size datasets but only finding out after you've put major effort into adoptionv+integration isn't really easy for someone working with data when you have something battle tested like Postgres et Al.