I see a lot of '68-'74 Citroen DS at the front, a lot of Porsche 911 at the back, and the glass and c-pillar remind me a lot of the Mercedes-Benz CLA and CLS as others have noted. I think this looks quite a bit better than the CLA though; they cut a lot of the visual 'heft' of the CLA out by having bigger wheels & tires.
The proportion of sheetmetal between the bottom of the beltline and the top of the wheel well is much smaller in the Ioniq 6, making it look a lot more svelte to me.
I watched a YouTube video about the car yesterday:
At 12:50ish he has a seat inside it and there's
loads of headroom, unlike the CLA/CLS. I think they've managed to make this car look a lot sleeker than its actual dimensions would have you believe. Not unlike the Ioniq 5, which inch-for-inch is actually a pretty big car on the spec sheet but doesn't look it in person.