This app was mentioned in 3 comments, with an average of 1.00 upvote
I'm always on the look out for good puzzle games. This one is the best one I have found in a long time. 190 levels.
It is similar to Crystalux but with a lot more variety and a more liberal puzzle unlock policy.
One IAP to turn off ads, and a few more for hints, which I have ignored.
Here is one of them:
https://play.google.com/store/apps/details?id=com.icecat.hex
It has more puzzles, and you can try out the first 30 or so for free.
Still trying to find the second one.