A viral post has gone up on X that indicates that Giancarlo Stanton referenced his former teammate as a reason why he's got a new look. He's leaner, slimmer and aiming for better health in 2024, so he's adopted a bit of a new look than the domineering physicality he has had over the last few years.
According to the viral claim, Stanton's slimmed down physique is down to a former teammate of his:

“I had to look myself in the mirror. Do I want to be slow and run into 30 or 40, with 170 strikeouts the rest of the way, or do I want to be like Isiah Kiner-Falefa, driving balls into the ground, always making slow, soft contact, benefitting my team more. I choose IKF.”
The post seems to indicate that Stanton was offering a bit of a tongue-in-cheek complement to Isiah Kiner-Falefa, who recently left for the Toronto Blue Jays. Is this the case?
Did Giancarlo Stanton mention IKF for his new look?
No, Giancarlo Stanton never made this quote. He has slimmed down a bit and is altering his physique, but he did not credit, compliment or slander Isiah Kiner-Falefa. This is from a known parody account. New York Porch Sports is a comedic X account (formerly Twitter) that looks to fool fans into believing outrageous stories or quotes.

With the addition of Twitter Blue from Elon Musk, they were able to buy a blue check mark. Those used to indicate verification and were present on major news outlets, which is how people can be fooled. They're also intended to look like the New York Post, but they are not a legitimate news outlet.
The New York Yankees slugger likely did this to improve his health. He's been hurt very often, and some people believe his physical stature doesn't help that case. He hasn't said exactly why he did this, but that is a more reasonable explanation than "he wants to be like Kiner-Falefa." He's a slugger and not a defense/base running player.