i built my daily driver with QMK [0]... it has 9 buttons, most bringing per app specific custom pie-menus with Kando [1]
the design respects the most neutral position of the human arm anatomy, which lies between a slant angle of 20° up to 30° [2]
[0] https://www.reddit.com/r/ErgoMechKeyboards/comments/1jksi0x/...
[2] https://www.jospt.org/doi/pdf/10.2519/jospt.2004.34.10.638