In 2016, KM were obsessed with arm wrestling. More specifically, Jimin constantly “challenged” Jungkook even though he clearly knew he would lose every time. And JK just went with it because of course he would.
By late 2016 into 2017, Jimin retired the arm wrestling shtick and started looking for other excuses to hold JK’s hand.
And as you’ve already mentioned, if you look very closely, you can see Jimin’s small hands kind of..lingering sometimes. I’m not gonna say outright that they’re doing this intentionally just to hold hands but.. I mean, come on.