Via browser on desktop or mobile, you can play a nice selection of featured carts here: https://www.lexaloffle.com/bbs/?cat=7&carts_tab=1#sub=2&mode=carts&orderby=featured

Another list here:
https://nerdyteachers.com/PICO-8/Games/Top200/

I believe there are other ways to store and play the carts across other platforms, but you'll need more help than I can give you on that stuff.

On Lexaloffle, under the web player of each game, there's a pink cartridge icon. The image that opens is the cartridge - download it and load onto your favorite emulator.

Itchio also has a bunch of those games, and iirc they have a tag for PICO-8 games as well.

Also also, iirc the cartridges can be converted to Android's native format. And I'd need to confirm, but maybe HTML too, which if possible, would probably let for the game to be run on JoiPlay.

This is kind of a side note, but in addition to Pico-8 I also recommend checking out TIC-80. Has an Android build on F-Droid.

It is a platform very similar to Pico-8, but it also has integration to the website where people post their projects. Just type "surf" to browse and download and play games automatically.

The RP5 can run Rocknix, which is linux operating system that natively supports Pico-8 and Portmaster. I'd highly reccommend checking that out, it runs completely from the SD card and allows you to keep Android on the system memory, making it possible to boot either OS.