There's often a skill that seem interesting, but I can't see doing anything for me in my day-to-day life. What have you learned that was a lot more effort than the payoff was worth?
There's some debate to have here about neuroplasticity and whether cursive handwriting (or the process of learning something involving both the cognitive resources and some rather fine hand, wrist, fingers, a bit of an arm movement), but one thing is certain: it's a faster way to write stuff down.
I have tried journaling and other writing both in printed and cursive, and the former makes me not write at all, because there's not enough time in this world for me to be my verbose self on paper when trying to write legible printed letters.
Cursive is just that fast. Faster if you learn to write shorter forms of the same words. Even faster if you learn some special systems, but that's a different rabbit hole.
But I will admit that learning to be concise with one's words without losing meaning and gravity is also beneficial, even if only for trying to push Alzheimer's and others further into the future.