Yes, it was real. And yes it's now gone from the Oval Office. According to a 2017 New York Times article, Trump would consume up to 12 diet cokes per day while in the office.

Source: Nextar Media Wire

(NEXSTAR) – The furniture and artwork may be largely the same, but one ornament has apparently quickly disappeared from the White House Oval Office following the inauguration of President Joe Biden.

In the early days of the Donald Trump administration, reports surfaced that the 45th president used a red button atop a small wooden box to summon his caffeine fix.

“With the push of a red button placed on the Resolute Desk that presidents have used for decades, a White House butler soon arrived with a Coke for the president,” the AP wrote in a 2017 profile.

Later reports confirmed the box’s purpose but suggested the president was actually a Diet Coke man.

It appears getting rid of the so called “Diet Coke button” was part of President Joe Biden’s day-one agenda, as media images have surfaced of the 46th president doing business without the handy button or a can of Coke.

President Biden has removed the Diet Coke button. When @ShippersUnbound and I interviewed Donald Trump in 2019, we became fascinated by what the little red button did. Eventually Trump pressed it, and a butler swiftly brought in a Diet Coke on a silver platter. It's gone now. pic.twitter.com/rFzhPaHYjk

— Tom Newton Dunn (@tnewtondunn) January 21, 2021