I'm going to throw my 2c in here with my current experiences with my 2019 Hyundai Accent 1.6 GDI.
Now it only has 24,000km so far but is half way through its 2nd oil change.
Here in Australia the service intervals are set at 15,000km or 7,500km under severe conditions. Yes, nearly 10,000 miles on ALL non turbo GDI engines using dealership Dino!
I dropped the factory fill at 4,000km because it was very glittered with Al. The oil was fairly dark, not too bad but there was no way it was staying in for another 11k!
That was replaced by myself with Nulon full syn Euro 5W30 and a high efficiency Ryco SynTec filter. This fill went the next 11k until service time. It was pretty dark and did have a slight fuel smell but nothing more than my other two older MPI engines, plus all metal particles were visibly gone.
My dealership has agreed to let me supply my own oil so my choice from here on is Castrol Edge 10W30, which meets the specs, and I feel the fewer VIIs may make for a more robust oil and help lower its volatility, although I know some would argue it may have a lower quality base.
Either way I'm happy since they knock $50 off per service, and I can pick up a bottle of Edge on sale for around $40 which is better than what they would put in.
I'm about halfway through this OCI now (due at 30,000km) and it is starting to look dark, but I'm not letting it put me off! With the amount of driving we do (70% hwy, 30% city) I don't want to be taking it to the dealership ($207 + oil) every 2 months or so to keep it at that 5k mile mark! I am willing to keep a close eye on my somewhat extended (but recommend) OCIs using a decent synthetic...