Here’s a 4x4 MIDI controller matrix based on a Pi Pico
A clean design with a window for checking on your Pico.
This design clearly needs to be able to store multiple matrix setups, a long joystick press could enter the preset selection mode, in it’s simplest form there would be 16 matrix storage slots (perhaps changing the button number color to indicate the current matrix)
(In the demo she is playing her 30 solenoid powered Xylophone you can make out in the background)
She has other Music vlog posts.
Detailed Adafruit video and part links, crediting Liz above for software.