I work with two women, who officially became empty nesters over the course of this school year. They expressed doing quite alright by it. It's an adjustment.
My maternal grandparents didn't officially become empty nesters immediately due to caregiving my aging great grandmother. After, they took numerous road trips, to see various horse race(harness) tracks up and down the East Coast. That was a shared interest.
It's truly about rediscovering your life plans.
Some people, redo their children's room into dens or work rooms, art rooms, whatever the hobby of interest was. Then await the grandchildrens entrance into life
Warm wishes!