My retired friend and I talk about this a lot. I retired TO something: pursuing my art, writing, pickleball. I actually am less socially isolated now than when I was working, not even accounting for 2+ years of working from home during COVID. I was a lot older than coworkers in the last 10 years of jobs, and not into the whole work friendship thing in my 60s. Now I socialize 4 days a week via pickleball and a fiber group. Do online art workshops. Volunteer at the library and elsewhere. Meet old friends for dinner. None of which I had time for when I was working. The very best thing is making my own schedule and working on things meaningful to me.