Firstly, you need to look at the outstanding games of this genre. Beat Saber, Hi Fi Rush, BPM, etc. Once you understand how rhythm games work, you need to decide on the genre (shooter, RPG, action, etc.). After that, you need to decide on the genre of the music itself (rock, pop, beat, dubstep or phonk, etc.). This is a rather complicated genre, and it will be extremely difficult to create a rhythm for the game on your own. Unless it's a pixelated platformer. By the way, platformers are good to make on Unity, there are many tutorials and templates.
At CodeIT, we have even developed a virtual office in the form of a game, where we often relax, listen to music, and even play games within the game, so to speak.
To reach a goal, you first have to find it. I wish you success!