Yes, this is a known isssue. Youtube has the same problem. It doesn't exactly feel modern to try to "write" search input using the remote when there's a perfectly good keyboard available.
To my understanding, keyboard support must be enabled by the app developes themselves, i.e. Samsung's hands are tied if a developer (e.g. Spotify, Google) has chosen not to support the keyboard as an input device.
So, Spotify, please fix this.