Is there any way I can remove the play/pause toolbar in Preview app ? I don't use it, so it's annoying to see it pop up now and then.
No option are yet available to hide or disable this Play/Pause toolbar — This feature was introduced in macOS Big Sur and still here in macOS Monterey when you enter in fullscreen mode in Preview (even after many disagreements from users about this toolbar).
The only solution if you still want to read your PDFs using Preview would be not to touch your mouse or trackpad at all but only use your keyboard to navigate between pages.
However, there are of course many other PDF viewers and editors that you could try; many of them free.
You can also provide a feedback to Apple regarding this feature via this link https://www.apple.com/feedback/ selecting your device and hope for it to be manageable in the Preview settings in future macOS updates.