Hello! I played your game to the finish, nice work on your first game! I liked your main character and its idle animation, and I liked how you used a limited, harmonious palette. I also thought the platform-enemies, with the upward- or downward-facing spikes, was a creative twist on the idea of a platform - nice! The platforming also played relatively smoothly, with no bugginess, soft-locks, etc. The dialog menus were also nicely presented and smooth.
Some feedback that I hope is helpful:
(1). It felt to me like there was quite a bit of blind jumping here, meaning that I had to jump without knowing where my landing spot or enemies overhead would be. Players usually get frustrated by blind jumps, as it feels "unfair" -- if I jump and immediately die from touching an enemy overhead that I couldn't see, it feels like more a matter of luck than platforming skill. I think much of that results from the fact that your player-character is quite large relative to the size of your screen. If you think of games like Celeste, Hollow Knight, or NES Metroid, you could probably stack 10-12 of the characters on top of eachother on a single screen, which means you have lots of room to climb, fall, attack enemies and make big jumps that can all be seen on-screen.
(2). I would introduce the basic controls -- how to select from your start screen, as well as movement and jump -- on your game page, or on the start screen. You might also consider keys that fit naturally with the hand. For players who like WASD movement, using Z and B is difficult; for people who like arrow movement (like me), the Z and B feel unusually spaced apart, and require me to do all jumping with my pinky finger. (I'm assuming a QWERTY keyboard).
(3). Consider a "fail" animation when you hit an enemy, before restarting the player. Being instantaneously transported to the last checkpoint when you hit an enemy is a little jarring, and it also doesn't allow you to see and digest how you died.
(4). If it's a fit for you, if you're looking for comments and feedback like this, consider game jams, where you will typically have more people playing your game, and more people offering opinions on it. Ranked jams, in my experience, tend to get you more comments/feedback than unranked ones.
Nice job on this!