In Chrome on your Mac: plug the OP-XY in with USB and press com, then T4 on it, then Send to OP-XY. Afterwards press T4 again, switch the OP-XY off and on, put Pocket on an instrument track and pick one with Game.
Sending needs Chrome on a computer. Here you can Download a game and copy it to samples/pocket/ on the OP-XY yourself, named game1.wav (or game2.wav, up to game8.wav).
Your own game
A .gb file up to 512 KB. A colour game plays in grey if it also runs on the monochrome handheld; colour-only games won't run. Only use games you're allowed to: your own, or free ones (Homebrew Hub, hh.gbdev.io, lists many with their licences). Your file stays on your computer: nothing is uploaded.
Playing
The OP-XY's keys are the handheld's buttons, in any octave (Pocket's own screen shows the same map, and lights the keys you hold):
On Pocket's page: the first knob (the dark grey one) is Colours, and the fourth (the white one) is Game (1 to 8). Sound plays too, on instrument tracks 1 to 8.
Licences
Each game is its makers' work, shared here unchanged under its own licence. Thank you to everyone who made them.