If there is no rotate option available for displays connected through a dock, check that DisplayLink software is installed.
If the DisplayLink Manager is installed do the rotation through that instead of using the System Preferences: Displays rotate option (which is not available). If this fails, check the DisplayLink software is fully up to date.
I usually write a blog post about once a week. The latest post can be viewed here: What Is Anything?: Use language in an honest way to communicate instead of obfuscating. (posted 2025-08-07 at 20:27:52). I do podcasts too!. You can listen to my latest podcast, here: OJB's Podcast 2025-07-18 Too Many Road Cones: I think it is clear, there are too many road cones!.