There's a lot of handheld game consoles out there right now for indie game devs. It's an exciting time to carry a game in your pocket! But it's splitting the community.
My proposal: learn how to make Game Boy games! Almost every one of these devices can play Game Boy games, and there's lots of resources for every skill level in the homebrew scene!
Advanced: https://github.com/gbdev/awesome-gbdev/blob/master/README.md
Intermediate: http://www.dotmatrixgame.com/
Beginner: https://www.gbstudio.dev/
@bunnyjane in my NES (and now also SNES) development I've always been really amused at just how many platforms I can just drop my games into and play on. I personally prefer those two over Game Boy due to screen size and processor choice.
I definitely agree that homebrew is a good workaround if you intentionally want to run your games on these devices. Big advantage in being able to run on some device without expecting the player to learn how to compile your thing. Just a ROM and that's it.
@NovaSquirrel Do you have any good links or advice for how a complete newbie could get into programming for the NES?
Promoting the GB is a little selfish on my part. I have an ODriod Go. It runs GB games better than NES and can't run SNES at all.
@bunnyjane I do have a few pointers even though I don't know of a single best tutorial to link people to.
https://mesen.ca/ is the best emulator because it has amazing debugging tools and tries to be very accurate
http://wiki.nesdev.com/w/index.php/Nesdev_Wiki is a great overall reference but doesn't have much in the way of an actual tutorial
Tutorial-wise I've seen https://nesdoug.com/ and http://nintendoage.com/pub/faq/NA/index.html?load=nerdy_nights_out.html linked to but I'd say don't get too attached to the tools they're made for.
@bunnyjane I would also recommend just getting in touch with other people via https://discord.gg/sthFzMS or http://forums.nesdev.com/ too. That'll help a ton versus trying it all on your own.
https://github.com/pinobatch/nrom-template and http://forums.nesdev.com/viewtopic.php?f=2&t=17295 are good sample projects worth looking at.