Cool to see that you're dipping your toes into unity! Here are some things I noticed: The main menu and restart screens background doesn't scale with the screen (just go into fullscreen and you can see the default unity background). There are options on the image's rectTransform that will allow it to scale with the screen. Also while the volume slider works, it only works within the options menu, leaving back to the start screen will not change the volume elsewhere in the game. You'll probably want to use a singleton for that.
As for gameplay, although the camera movement is cool, it really bamboozles me, as when I press A/D, I expect to move left and right. This is even more apparent when you start moving a bit and then rotate the camera; in that situation, if I try to move forward or backward, my previous velocity is unaffected; If I don't want to roll off the platform, I have to go to the hassle of first undoing my previous camera rotation, then moving in the opposite direction. Maybe you could put camera movement on the mouse or just have it slowly rotate constantly? Worst case, just increase the rotation speed to compensate and maybe add some more friction.
Otherwise, just keep at it, it'll all come with time!