Amazing game!
Soothing music paired with a relaxing theme of growing flowers and the right difficulty puzzles . A truly amazing combo! I have a few suggestions, but they aren't anything major, just details I noticed:
You can't delete the teleporting mirrors by right clicking the second one, only the one placed first.
Most of the mirrors are two sided, which is great for readability. If I were you, I would considering making the reflecting and teleporting mirrors also two sided. At a quick glance, it shouldn't interfere with the puzzles too much, if at all and will make distinguishing and placing (only 2 effective orientations to cycle through) them much easier. I do applaud the cute lantern solution tho.
The tile, from which the plant starts growing stands out from the rest. Could possibly be a sprout growing from the center of the tile right to the edge? Same thing with the dirt cubes, I don't have a clear idea for it tho.
I can share a "hack" for backgrounds: Godot has noise textures 2D. Either overlaying a Sprite with that texture and high transparency (modulate) or writing a simple shader for a ColorRect (take normal colour and noise, if noise black -> make colour slightly darker, if noise white -> make colour slightly lighter) makes it look a ton better without actually drawing any assets.
Initially I was sceptical of the tutorial revealing pretty much whole solutions for the first levels. However thinking through it, I fully support the decision. It's the only reliable way I can think of to get the player accustomed to the unusual controls and grasp the orientation aspect. There are also plenty more puzzles for the player to solve on his/her own.
I REALLY enjoyed the game, want to say that one more time. I hope this could be a small contribution to it.