For at least the first couple of years, I'm changing my oil twice a year, even though I don't put on a lot of miles (and **** few ICE miles).
The owners manual suggests oil changes every 7500 miles or 6 months, whichever comes first.
I did my first oil change at about six months, even though I had less than 3000 on the car (and about half was EV miles). One reason why I felt that the expense was justified was because it's a brand new engine and in my book, any brand new engine should get its first oil change much sooner than the standard interval, due to concerns about possible debris in the engine left over from the manufacturing process.
Another reason was because guess what: Kia is currently facing a class action lawsuit for several models (which, as far as I know, does not currently include the Niro) because of fires and premature engine failure, apparently arising from a problem with manufacturing debris left in the engine that plugged up the ports where the oil circulates. I have no reason to think the Niro has a similar problem aside from the fact that Kia apparently made this mistake with other models.
Another reason was because the Niro PHEV is a really new model and there might be bugs that will shake out in the years ahead and if that should happen, I want to be on really solid ground with respect to my warranty compliance.
And another reason was because I use my PHEV in a way that is probably somewhat atypical: I go for months in almost 100% EV mode, infrequently starting the ICE. While that's probably mostly good for ICE longevity, there might be some unexpected consequences that arise from using the ICE in that way, so here again, I want to hew close to the warranty requirements.
I imagine that along about year three, if my driving habits are still the same and I haven't heard anything awful about the Niro with respect to the ICE and lubrication in the interim, then I might drop back to the 12 months schedule.
2018 Niro PHEV Gravity Blue