Yeah I quickly realised that it wasn't ideal if you had to look up and down between the screen and your keyboard, so I added the ability to use your mouse. Which also solves the issue of different keyboard layouts. Indeed most levels only have a limited amount of possibilities. However, this is also to make sure that the player has some guidance. I don't know if you've played level 9, but that level is quite difficult because there are too many options and there is no previous explanation of what to do when there are multiple starting keys. With each level I tried to teach the player a new trick that they could use in the level after it. Like level 5 shows you that towers are more effective if you circle the path around them, you then use that knowledge in level 8 and 9. Level 6 introduces the wall key and the radial tower, then level 7 expands on those lessons.
I agree that the implementation of the trophy system isn't great. It was meant to give players an incentive to replay levels and to create extra difficulty for those that wanted it. It would have been nice if players were told whether or not they got the trophy at the end of each level. Since players are now only made aware of it in the level select screen. Making it count down and turn red might just confuse the player. Perhaps creating a limit for the amount of keys that can be used is a good idea, something like the minimum + 5. Currently you can enable as many keys as you like, then the pathfinding system determines the shortest route using the keys you've enabled and the amount of keys it uses determines whether or not you meet the requirement. If you're interested, I made a devlog showing the solutions for every level and what I intended for the player to realise in each one.