I can only say what worked for my DW and I, when we retired 25 years ago.
My intent was to live on the top of a mountain, with barbed wire around the perimeter. Enough of business and co-workers, and really, enough of the people in our neighborhood. They were nice, but not retired.
For starters, we couldn't afford world travel, or golf club memberships.
After the initial settling in our campgrounds, with other relatively young retirees... we went to Florida, and looked at at least 30 different senior parks... (note: not all senior parks require the age 55 minimum, but often require 80% to be 55 or older, and only one person of a couple need be 55 in the "all senior" parks.)
Not being super social at the time, the park we picked out WAS social. It took about one week of living there, to know many people who were (as were we) in their early 50's, and another month to know almost everyone in the 350 home park. With everyone being retired, and in our case, in a similar socioeconomic position, it was a case of looking for happiness, so, between hobby groups, singing groups, billiards, shuffleboard, bowling, boats (our own marina), the pool and hot tub, and a minimum of one party a week for the whole park, it was a case of picking and choosing. Just too much to choose from. A wonderful problem!
It's no different today. The people are different, but the park is still active, as young people move in, and take over the social organizational management.
Yours truly became a party emcee, the computer class instructor, and more or less in charge of organizing the group trips to Daytona or Orlando or Cedar Key. DW was into line dancing, country western dancing and pool exercise. Plus we had our own little group of couples for cocktails and dinner at each others homes... that met once a week. That lasted without missing a meeting for over 20 years. Different folks as people moved or drifted away. 20 years of weekly get togethers count for a great social life, and forever friends.
Life after retirement is what you make it. For sure, it changed my plan to live in a cave. I DO believe that a new start... like moving and finding people that share your retirement hopes, is a great way to explore a new social life after retirement.
BTW... I never danced after our wedding until we retired... 30+ years later, and now we rarely miss a dance.
I am so happy that we didn't hunker down in our Chicago suburb home, with a one or two day a week meeting with a church group, or the twice a year neighborhood barbeque.
Would this work today? I think so. For those who have moved into our Florida Snowbird community, I know so. The age spread may be a little older, but the spirit and the action is no different. Ask the convertible club, or the motorcycle group... and ask the party goers, who never seem to get over the band, the kegs of beer, endless wine and hors d'oeurves, for $6/person.