I did some research and found a few options, copy-pasted from my reply in another thread!
micro:bit (they're like $20 aka CHEAPER than a real Tamagotchi) you can also do this with the Arduino but that is $$$
OpenTama if you're the smarty-pants who can just....magic computers together (smth smth solder???)
https://m.elecrow.com/pages/shop/product/details?id=207465& this is a Tama DIY kit for $10 but idk how to make *gestures to all that* into a *holds up old dingy Tamagotchi* (3D printer crowdfund plz)