Idk if that’s a feature keyboards have or if it’s more on the os side

Florisboard, openboard, anysoftkeyboard

No clue, sorry. Looking at the list, I’d go with “multilingual thumb-key” or just thumb-key. Messageease is the proprietary keyboard thumb key is based on, and I think more thought has been put into making even more optimized layouts for thumbkey, so I’d guess the messageease one is a bit outdated, and I think there might be a two hand mode that “type-split” is for but idk

https://github.com/dessalines/thumb-key this can be pretty quick once you get used to it