This. I am baffled by friends and family that talk about how they couldn't retire because what would they do? My response is to list the many, many things I want to do that I can't because I 'have to work': read more, learn new languages (spoken & computer), take up the piano/guitar, try new games (board, tabletoprpg, computer), write, program, etc.
The only reason I ever get bored is because I don't have the time, resources, and/or other people to do what I want. The thought of not having to rely on a work schedule to provide necessary resources sounds wonderful, not threatening.
The last couple of vacations I've taken have been staycations. Even though I have many hobbies and interests - several musical instruments, writing music, drawing, dabbling in code, reading - not having the structure of a job and expectations of others weighing on me to 'be productive' I procrastinated quite a lot. I frequently felt anxious and unfulfilled. I took this experience as a glimpse into what retirement might be like.
In retirement I think I'll need to create a schedule for myself that includes having others depending on me to 'show up'. E.g. doing volunteer teaching, etc.
I've noticed it's really difficult to work on side projects also when you're in between jobs (especially if you don't have much saved up) because the looming threat of financial ruin never lets you forget it, and you just get too distracted by it that it's hard to be productive even though you have so much more time, and every moment you spend on side projects your brain goes "you could be putting this energy into looking for a new job right now."
I know that's probably different than your staycations, but it's for that reason that I don't think I will be as bad at working on my personal projects once I've retired (if I ever can retire).
I've found that when I've been stressed out or overly busy, it can take a while to adjust to a more relaxed rhythm. At first I just want to slack off completely. After a couple of days, this gets boring, but it takes longer than that for my motivation to come back.
Last year I was unemployed for about a month, and it was really only near the end of that time that I started to get some momentum going with side projects and hobbies.
I've recently started scheduling stuff I'm doing in advance and trying to stick to it, and I found it incredibly empowering. I too ended up wasting a lot of free time despite having a growing bucket list of things to create - scheduling free time helps to overcome that and generally makes me happier. I hope to use the same technique if/when I retire.
I think this is a change that cannot be done just after retiring because the mindset is not prepared. This is something that has to be cultivated during years so when the moment of retirement comes, you keep doing your alternative things instead of wondering "what should I do now?"
It's not all rainbows and sunshine - my brain likes to be _interested_, so as soon as I feel a challenge is "figured out" (even if it's incomplete) I tend to move on to the next thing.
So it's easy for me to be engaged, hard for me to complete anything.
The only reason I ever get bored is because I don't have the time, resources, and/or other people to do what I want. The thought of not having to rely on a work schedule to provide necessary resources sounds wonderful, not threatening.