Can't set external monitor's maximum resolution

Hello. Brand new Razer owner and brand new member here!

I bought a "Razer Blade 15" (Mid 2019) - Advanced". It has an in-built "GeForce RTX 2070 with Max-Q Design" graphics card. I've just now connected the laptop to my external monitor, a Dell U3011, capable of 2560 x 1600 resolution. It's connected aith an HDMI cable. However, I can only set the second display to 1920 x 1200 - there is no higher setting.

I've spoken to GeForce support and they say (and their web site's specifications page confirms) that the card is capable of a whopping 7680 x 4320! But they say that the actual maximum setting is up to the laptop's manufacturer, so they've pointed me at Razer.

I'm really REALLY hoping that my brand new several-thousand-dollar laptop can drive my external monitor at it's max res of 2560 x 1600. If so, how do I set this?

The card's driver is Provider NVIDIA, Date 29 Jan 2020, Version 26.21.14.4219.

Thanks!