I believe that unless one manages to regress to our primal animal state the brain has a need to think about something in order not to think about self and the possible dark existential stuff which should absolutely be ignored and avoided.
In this scenario the best possible way to occupy the brain is to set goals and build discipline towards reaching such goals.
Even pleasurable stuff like music or social connection or even I'd go as far as sex might seem 'not work' on day-1 after you fire yourself after receving the 10mil cheque
But On day 60 after leaving work with 10m
1) the 'fucking around' on the fretboard becomes 'practicing scales for at least 30 mins'
2) the hanging out at the bar becomes 'organizing parties in a way to maximize social fun with games etc'
3) the 'ONS from the club' becomes 'trying to find an escort with girl-next-door look who'd also offer Pornstar sex service and greek sex service'
Every human endevour of any kind has an S-curve type shape where after a while if you want to progress and get novelty from higher experiences you must apply IQ and discipline and so it becomes a 'work'
Leonardo Da Vinci after having signed off all the accomplishments that we know basically turned wedding planner and party organizer in Milan , I suppose orgy organizer too but don't quote me on that, and guess what? After 60 days or so it became a 'job' for him to put the pieces together in a way to reach an amazing social result.
Same with today marriages, happiest day of her life? It's the most work of her life too to get those 8 hours or whatever is the party lenght exactly right