It's actually more efficient at highway speeds to run the ICE so I hit the HV button when I'm up to speed, then on my way home switch to EV when the mileage on the guess-o-meter is around the same miles to get home.
As pointed out in the other responses, as a general statement driving in EV is always more efficient than gas, including on the freeway. And for most people it will be more economical also, especially when gas prices are high.
However you are bringing up a scenario where you will be using all of your EV range during the trip and the rest will be using gas. That brings up a separate topic which is whether someone should manage EV use in those situations. Many people including myself will start out EV but then switch to HV for at least part of the higher speed freeway/highway driving, then switch back to EV when there is just enough range to get home, just like you are doing.
As for me I do this just for ride enjoyment, and I think that is likely true for others also. On city streets I like the near silence of the car, I don't really like hearing the engine when I accelerate from a stop. However at freeway speeds I barely hear the engine over the wind and road noise. So I prefer to use HV on the freeway and EV on city streets, and that seems to be a pretty common strategy. Although if you say that some people will say "You're overthinking it, just drive the car it knows what it's doing". Well sure you can drive it that way also, let it use up all of the EV range at the beginning of trip and drive HV the rest of the way. If someone finds it too much trouble to switch back and forth from EV to HV, and they don't mind engine noise on city streets, then I fully understand that some people prefer to drive it that way. It's all about preference.
However there is also some opinion that switching to HV on the freeway in these situations will also make the overall trip more efficient, because EV range gets used up pretty fast at high speeds, whereas the gas engine at steady highway speeds will go into direct drive mode, which is basically an overdrive gear. It's the only time the gas engine directly turns the wheels, all other times it just generates electricity which is then sent to the electric motor. My guess is this makes it a little more efficient to use this strategy. However I suspect it's not a huge difference, so it still comes down to mainly being just preference.