Yes, you can use 2 4G SIM cards at the same time in Nokia 8.1.
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.
Yes, Nokia 8.1 does have the USB Type-C port.
Yes, with Nokia 8.1 you can record 4K videos @ 30 fps.