i'm about to order this but was horrified at the expense of the extended components which require adding a reel for a fee of around 6 euro per reel last time i checked. the csv and bom file generation was beyond me so i'm gonna put up with it. here's a few suggestions anyway.

replace r1 39 ohm resistor with a pair of resistors 49.9ohm and 180ohm in parallel for 39.3ohm these can be sourced in 0603 size.
likewise replace r3 and r4 with a larger size.
remove sw1 and sw2, these can be hand soldered.
I have edited the bom and csv of the last two and shaved 5 euro off my order. i cannot easily change the 39 ohm resistor.
i won't complain about the voltage regulators because they are an ephemeral purchase, but come on, 5 euro for a resistor is far too expensive.

The below parts won't be assembled due to data missing.
J1,J2,H1,H2,H3,H4,U2 designators don't exist in the CPL file.

I think that you could add a 3.3k pullup to 3.3v on each button header. this would prevent the double click bug from occuirng by providing at least 1milliamp wetting current to blow through the oxide on the switch. this is specified in the omron datasheet as required to ensure reliable operation.

there's a boring video here about it. https://www.youtube.com/watch?v=v5BhECVlKJA

When I try to order from jlcpcb, a few of the parts look like they're loading in the assembly the wrong way around

Tried to build the code and got a warning
warning: implicit declaration of function 'sleep_us'

It seems like you need to include in pmw3360.c
#include <pico/time.h>

BTW Really great project