Wow that's a big one. It's always nice to make something for a sibling.
Did you run DRC? You seem to have a couple unconnected nets: 3V3 between pico and U1 & the boot/reset switches, and also the ground of SW13. See attached images.
It also complains that pad 5 of SW14 is unconnected and while it technically doesn't seem to be, you can fix the complaint by redrawing the connecting trace and making sure it snaps to the center of the pad.
You might find routing easier if you use pours (e.g. fill the entire board on one side with ground and on another with 5V or more ground).
I hope you've accounted for the size of keycaps when designing that layout. Your key spacing looks relatively standard at ~19mm, but there's a small risk that the corners of a cap will bump into an adjacent key when you have keys that are rotated relative to each other. Of course, that's nothing a dremel can't fix (I have a pile of mutilated keycaps waiting to be cleaned up with a knife...).
One more thing to think about is whether you want some kind of mounting holes. Maybe you'll make an enclosure later, or at least add some rubber feet so the bare PCB doesn't scrape your brother's desk with all the pointy through-hole component leads. Of course even without mounting holes you could always stick some adhesive backed feet to the bottom of it.
Also you'll still need to figure out how to generate gerbers and drill files. Then we can appreciate the board on tracespace.io :) And you might pass these files to your fabricator (unless they ingest
kicad pcb files).