There's one on the Play Store (eww, I know) by Redstone games that ive been using for years. No third party data sharing and minor data collection. No login required and it runs fine with network disabled, you'll just need to allow it on network if you want new puzzles, though it comes with MANY.

Also, on the difficulty note, I find people around me tend to enjoy helping. Its become a bit of a ritual in the evening for my partner to help me with tough clues. Great for car rides too (passenger on the phone, obviously)