On desktop, I use the AI-designed Halmak Keyboard, and its had great results.

Rather than manually picking letter positions, Halmak was designed by an evolutionary algorithm, based on a given set of criteria, and sample text.

I designed the original english thumb-key layout manually, with trial-and-error, and based essentially on 3 criteria:

• Letter frequency
• Alternating thumbs
• Thumbs come from the bottom corners, so lower and edge tiles are easier than higher.

But I did not take into account things like digrams / trigrams, and I don’t know enough about evolutionary algorithms to do it.

Would anyone be interested in tackling this problem?