Retired person here.
It is interesting how the definition of Quiet Quitting quickly changed from being a hard working employee who finally decides that enough is enough and decided to give just a solid days work for a solid days pay, to: slackers, time wasters, retired on the job, unambitious etc.
It's as if the initial concept was too difficult to face, hard working employees who are burnt out. Making it slackers etc. makes it far easier to blame the victim.
I can give you an example of a Quiet Quitter and the exact moment he decided he had had enough. This manager had a long and successful career with the company and had done all the usual 'beyond the call of duty' stuff: stayed late, worked weekends all without overtime pay, travelled at short notice, missed birthdays anniversaries, graduations etc. because of company work. He was highly respected and a mentor to many junior employees.
The breaking point came one Christmas. The company had promised a new pre-production prototype would be delivered to the customer by the end of the year. Christmas came and, as usual, the company was late. This guy was asked to work from Boxing Day to New Year to get the prototype out of the door. He worked with eight hourly employees working 15 or 16 hour days. The hourly guys (unionised) had a choice of how they were paid: triple overtime or double overtime plus time off in lieu. This guy was paid nothing - his time was considered to be 'donated time'.
They got the prototype onto the truck at about 11:00pm News Year Eve. He estimates that he was at the plant for about 100 hours those days plus he had put in about another 50 hours unpaid overtime in the weeks before Christmas pushing things along. The Vice-President decided his devotion merited a special award: The company gave him a $500 bonus - equivalent to just over $3 an hour.
From that point on he stopped working unpaid overtime, taking work home, etc. He was no longer available to travel at short notice. He still did an excellent job at work, only now it stopped at 5:00pm.