https://www.reddit.com/r/EmuDev/ is a great place to hang out if this topic interests you. They'll always suggest doing CHIP-8 as a starter project but my unpopular opinion is to just attempt to emulate basic x86 programs [0].
Having written a CHIP-8 interpreter, I'd agree with the popular consensus to start with it. x86 is definitely more ambitious though, and would be fun if someone had the right background knowledge needed already.
I wrote my first emulator recently, for no particular purpose. I didn't choose CHIP-8 because, frankly, it was just too trivial. Instead I went with the Gigatron. Still pretty straight-forward as far as these things go, but you have to handle a VGA signal and 4-bit audio DAC at least. It's also just a beautifully elegant machine worthy of study.
[0] https://notes.eatonphil.com/tags/emulators.html