Yes, Thumb-Key - an open-source privacy-centered alternative to the better-known MessageEase input method.
Unexpected Keyboard is another open source and privacy conscious keyboard, with a couple extra features. It also makes use of swipes to enable more keys to be quickly entered.
It also permits custom layouts.
I haven't found documentation on how to use these, but I found reference to them in the thumb-key lemmy page, and found this very nice tool for creating layouts that someone made.
After being disappointed in the customization options of thumb-key layouts (just wanted an escape key), and having my suggestion to make it easier immediately dismissed, I used the tool to recreate the thumb-key layout, and hope someone can find it here and avoid that monotony.
In the settings for Unexpected Keyboard, press "add an alternate layout", and select "Custom Layout" at the bottom. In the entry box, enter the xml file contents from here and press "ok".
Now it should be set up. To see/use it, swipe up or down on the space bar to cycle through layouts.