Author of one of these "markup"-based toolkits here. I believe that Rust might not be the best language syntax to express UI. I am curious why you are so strongly against using a DSL.

This topic comes up often, so I wrote a blog post explaining why I think a DSL is a good fit: https://slint.dev/blog/domain-specific-language-vs-imperativ...

I'd like to have non-imperative gui code in Rust.

Why Rust? Because I like its power and with recent developments such as subsecond the compile times are absolutely negligible.