Great thread! It's good to know that I am not alone on losing ambitions of many sorts. I retired 1.5 years accidentally because my work culture become so toxic that impacted my health. I didn't dream too much about what I'd do after FIRE, which I don't recommend.
My biggest hobby used to be painting. Comparing with prior FIRE, I do less painting because painting gave me a voice and a balance over my stressful job.
What I do more: hiking, volunteering, reading, resting, learning finance, watching TV, dancing, traveling, seeing my family in China...
What I do about the same amount: cooking, cleaning, writing...
What I do less: painting, getting with friends (because we moved 3000 miles away after FIRE), promoting my art...
My takes are that you will change (with age, health conditions, absence of a job, moving etc). You cannot prepare for all the changes, but you CAN start pivoting to live a life you want to live (through shifting the focus, a semi-retirement, part-time etc) and check out different things. Surprises are a part of FIRE's gifts (or curses). Many things don't work out as my imagination or plans. Then I learn something new about myself, adopt, and move on. Develop muscles of contentment and gratitude because they are the best antidotes for any changes.