Interesting question. I had the fairly immediate task of jettisoning my work-related stuff I’d never again need, and packing up the smidgen of that which amounted to memorabilia. Which now 2-1/2 years later I’m about to throw away as useless clutter.
Other than that, I can’t really think of myself at the point of retirement as having some backlog of projects. Maybe other than commencing all the long-delayed travel and recreation I’d wanted for the last 40 years, but been unable to do. Which pretty quickly led to the sub-project of leaving my mistake of a 2nd wife.
But as noted upthread, I’m a) terminally lazy, and b) having downsized, and rearranged, and lightened my life hugely compared to most retirees, there’s not much that needed or still needs doin’.
I guess maybe “downsized, and rearranged, and lightened my life” was my post-retirement project.