Update your nightly Rust toolchain to be able to use async functions in traits:

#![feature(async_fn_in_trait)]

trait Database {
async fn fetch_data(&self) -> String;
}

impl Database for MyDb {
async fn fetch_data(&self) -> String { ... }
}

https://blog.rust-lang.org/inside-rust/2022/11/17/async-fn-in-trait-nightly.html

utility patent law: we have so much jargon & nothing means what you expect it to mean

design patent law: lol we have a test called the "basically the same" test. it goes, do these two things look basically the same?