Apparently they did a long experiment with Stylex at Shopify and found that it was "a wash in every metric":

https://xcancel.com/argyleink/status/2095253698431844607

Linear adopted stylex as well and published a comprehensive write up https://linear.app/now/styling-linear-for-the-future-stylex

And it has an explicit LLM Resources endpoint: https://stylexjs.com/docs/llm-resources