In the current implementation of the matrix-js-sdk, setting the cache property of fetch() to no-cache (-> Cache-Control: max-age=0) prevents browsers from caching preflight (OPTIONS) requests. This behavior leads to unnecessary network overhead, as preflight requests are sent before every cross-origin request, even when the CORS policy remains unchanged.

https://github.com/matrix-org/matrix-js-sdk/blob/develop/src/http-api/fetch.ts#L294

The older implementation from 3 years ago doesn't seem to specify any cache-control directive on requests:
https://github.com/matrix-org/matrix-js-sdk/blob/e37aab29672256218d30876e96dd17fedc0506f7/src/http-api.ts

I'm not saying the new behavior is incorrect, but it's worth raising the issue and perhaps discuss it, as it has performance implications.