This is only partially correct.
Yes, you might only be technically using one app at a time, therefore there’s no actual direct multitasking as in two apps open at the same time on the screen.
But tvOS absolutely does utilize that extra ram to hold things open in the background, and it’s extremely noticeable.
I have both a 2015 and a 2022 Apple TV.
If you have two or more media player apps opened, every time you switch between them they will re-launch on the 2015.
Meanwhile, I can leave my 2022 Apple TV in sleep mode for several days, come back to it and everything is in the exact place that I left it.
If I was looking at a TV show or in the middle of watching a movie when I exited an app, chances are more likely than not that I’ll return to that app exactly where I left it on the 2022, even several hours or days later.
Sure, it doesn’t make as big of a change day to day as moving from an iPhone with too little RAM to one with enough, but it certainly still makes a difference.