Sometimes they post something on their blog site (https://www.roku.com/blog) but that's usually for a major version update. I just checked and there is a post about 9.4, but not the incremental update to 9.4.1. I don't even see anything on the developer web site. So my guess it's just some bug fixes. In general, they don't tend to issue release notes for version updates.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." If you appreciate my answer, maybe give me a Kudo.