"simultaneously show" is a correct and usable phrase in written English.
You can use it when you want to describe two or more events or actions happening at the same time. For example, "The fireworks display and the light show at the carnival simultaneously showed off the beauty of the night sky."
The medium allows its amateur historians to simultaneously show and tell.
I set up both projectors so they would simultaneously show "Wall-E" on a wall, with the images stacked.
High street outlets and online crafting websites sell feminist jewellery so you can express your feminist credentials and simultaneously show off your accessorising skills.
They note that they are building in or working on technology like voice commands and screens that can simultaneously show a map to the driver and a movie to a front-seat passenger, as in the new Jaguar XJ. "We are trying to make that driving experience one that is very engaging," said Jim Buczkowski, the director of global electrical and electronics systems engineering at Ford.
That means a publisher could simultaneously show a live video on YouTube, Periscope, Twitch and elsewhere.
The application includes support for Picture In Picture, which means you simultaneously show two streams at the same time.
And yet it has simultaneously shown zero enthusiasm for giving it up.
He exuberantly uses split screens, simultaneously showing Laramie and the landscape's harsh beauty while people talk about how they feel about the place.
Simultaneously showing us little Clara and the grownup woman she yearns to be, her dancing embodies the essence of Nutcracker magic.
These looks all managed to appear interesting and new in a catwalk-worthy way, while simultaneously showing off how trim the wearer's waist was.
The other, played simultaneously, showed Australia's prime minister at the time, John Howard, speaking two days earlier, urging his country's Parliament to do the same.
