Here, Embark new game engine in Rust hasn't gone anywhere,
https://medium.com/embarkstudios/embarks-creative-playground...
It even got a new release quite recently,
"we here at Embark been using this for over a year in production now for our Creative Playground & custom Rust engine that uses Vulkan, and hope it can be of use for more developers as we continue to build it out."
-- https://old.reddit.com/r/rust/comments/zrskiq/rustgpu_v04_re...
Yes they are also using Unreal for other titles, plenty of studios have more than one engine.