This is a great mobile game! I had a lot of fun taking a shit to this. I would suggest a few things:
First, I would assume the crowns are bonus items. Sometimes, the crowns are much easier to find than the goal. Maybe make it so that you have to complete a challenge that's slightly tougher than the goal, like a harder version of a previous puzzle, or maybe an upcoming puzzle. (I think you did that with the sequence blocks, which was fun)
More ways to play are always nice! Thank you for making this compatible on Mobile. I would suggest changing the controls from the touch pad controls you have now to swiping to move. It's self-explanatory and it saves space. While we're on the subject, this game in particular would be fun on an actual controller. Keyboard and touch is just fine, but having an option for Xinput would be a fun, albeit small thing to make playing games on here better.
If you were going for retro graphics, you nailed it! I noticed that from the music (which was really catchy), the SFX, and the fade transition, which all felt like an old NES cartridge. I also got some Atari vibes. As simple as this game is, I can tell you're talented in old-school pixel art.
Love that you can choose the color of your cube! If you're going to expand this game, maybe you can acquire points and be able to unlock patterns or other cool colors for your cube?
Maybe make some metals for this game? Creative titles/graphics for achievements are easily noticeable on someone's profile on this site and could convince more strangers to play.
That's all I have for now! You've done a good job!