The body can fast for as long as one has enough fat stores to provide energy and hydration, AND the environment is pristine enough to support the fast w out toxic loading.
I know of and watched others who dry fasted for 20 days.
Personally, I’ve dry fasted two weeks, no problem.
I’m on day 6, its really described perfectly well in dry fasting stages. You also need to build up a fasting muscle, which is important. Sometimes you have to start with intermittent and then move up.