I know that casting from Plexamp is fairly new, so I’m not sure if this is a bug or just an unimplemented feature.
I have 2 smart displays, a Nest Hub and Nest Hub Max. When casting to these from Plexamp I only get the options to pause or rewind/fast-forward 30 seconds. Other music players provide the option to skip a particular song, which is helpful if the device used to cast is not nearby.
Using voice commands to skip fails as well which also may be related to the implementation.
I feel like this is a pretty major function that should be available on smart displays like these.