Yo
level 6 plays beautifully now
and the amount of potential optimizations is insane
I after optimizing managed to beat it in 5 gates! (It's not the same solution as before) But it's not a kind of solution that a casual player would find, so you should be fine.
Now that I think about it level 5 is also kind of broken:
you can just not connect input 2 and XOR 1 & 3 and
the level is solved. To solve it I'd just change how 1 and 3 behave with each other ( Rn it's exactly the same as level 4 )
That's all
Your game is great
Have a nice day/evening!