On iOS there is Morse Machine, similar idea for single characters. There is also morse.camp, a PWA that focuses on recognizing English words.
On iOS, I like the Ham Morse app. It does Koch and Farnsworth, simulates QSOs, and sends news summaries.
Yeah, LCWO is the gold standard for Koch training on the web, and I'd second the suggestion for CW Academy. Having a commitment to learning with other people tends to help you ride out the rough patches.
To help with my own learning, I built a mobile friendly web app/game which includes Koch as an option. It's also open source - https://github.com/mdp/morse.mdp.im - morse.mdp.im
Interesting! I found myself struggling a lot on the linked site because the random groupings made it very easy for me to lose my place and feel like i've gotten behind, but LCWO's fixed groups of 5 help my find my place a lot better.
https://lcwo.net/
Which uses a similar technique. It also has quite a few more types of practice such as words, callsigns, games, contests etc.
I learnt Morse code there last year before I did a CW academy online course and I really enjoyed the approach.