The Skyactiv versions of the Mazda 2 (2014+), the Scion iA, and Toyota Yaris 2019-2020, are all, basically (there's a few distinctions but we'll get into it.) the same exact car, minus front end differences on the Mazda vs the Toyota Scion ones.
The 2017-2018 Toyota Yaris iA (mines the 2017 ^---^) is also the same.
The skyactiv mazda 2 is only sold overseas, not in the US. Scion (before Toyota yeeted that whole division) said "Hey that's a cool car, can we take it and make it look angry and a bit like the current actually made by Toyota, Toyota yaris, and sell it here in the US?" and Mazda was like "sure thing bro".
After Scion died, Toyota rebranded it as the Yaris iA(different than the Toyota made Yaris, keep that in mind when ordering replacement parts and such) for two years with only a base model for 2017 - 2018. In 2019 they dropped the iA, called it just the yaris, and made three different trims. You can spot them because they won't have the iA. They also introduced fog lights and a tiny bebe spoiler to some of those trims I believe. After 2020, they got discontinued due to poor sales.

fat Americans don't fit in em I guess. There was also a hatchback 2020 version, which I feel you'd be interested in since you spoke about the Honda Fit.
Now to get into the complexities (yaaay).
The overseas mazda 2 is slightly different. For whatever reason, mazda decided US gas was trash, and detuned it so it could run on regular instead of premium gas like in other markets. In certain markets it also runs a slightly higher compression ratio of 13:1 vs the US 12:1. On the bright side, this probably means if you take good care of it, I see these engines lasting 200k miles. I've seen some make it about that far. I have heard of transmission issues tho so don't skimp on the maintenance. It's also called the Mazda demio in some markets, keep that in mind when looking for parts.
To get into even more complexities, the Mazda 2 skyactiv outside the US has three different engines, and in various tunes. The skyactiv 1.5L Gas(the one the our cars), the skyactiv 1.3L gas (tiny bebe engine), and the 1.5L skyactiv diesel engine.
The 1.5L gas and diesel ones make about the same power but the diesel has more tuning options since it has a turbo. More diesels have a turbo in order to make any real power.
There's also a 4WD (not awd) demio in Japan. Which might I say is lit af.
Can I put performance parts from the 1.5L skyactiv mazda 2 they sell in some markets onto my car?
Maybe lol.
So are they basically the same thing?
Pretty much lol. They have some differences in sound insulation as well. I think the American ones have more.
Are the pre 2014 mazda 2's the same?
No

which is sad because they seem to have a lot of aftermarket stuff.
Is the Toyota made yaris the same as the skyactiv mazda made yaris?
NOOOO. They are completely different vehicles. Toyota made ones are probably gonna be far cushier with softer suspension if that's ur thing. As well as come with that Toyota reliability.
But yea that's basically it. I have adhd and dive way to fucken deep into this shit.
Did you know the 1.5L mazda miata ND has the same motor as ours? (except not exactly, as it has a much higher compression ratio, a lighter valves and other timing bits, a forged crank, variable valve stuff in the intake and exhaust (our cars only have variable exhaust valves), and other bits and bobs that let it Rev to 7500rpm and make 127hp)