Yes, you can use 2 4G SIM cards at the same time in Nokia 8.1.
Yes, Nokia 8.1 does support Qualcomm Quick Charge. It also comes with 18W fast charger.
Yes, Nokia 8.1 does have OTG support.
Nokia 8.1 comes with the Android Pie out of the box. You will also get Android updates for the next 2 years.
Yes, Nokia 8.1 does have the HDR10 support and you can watch 4K videos on Nokia 8.1. You can record 4K videos also.