Director Mark Mylod has given some answers in this article. Below are his quotes. For more details and possible answers to your other questions, you can read the complete article.

@Markoff said:

He said she is just eater/taker and then thanks to nostalgia (?) he changed opinion just because she ordered something (burger) he liked to prepare to go? It doesn't really make sense.

“Ralph’s character and Anya’s character are about connection,” Mylod tells us. “Ultimately, she has manipulated him. He also realized that she’s manipulating him but he allows her to win. All the unspoken business is in the final discourse between them and the burger. It’s a mutual understanding… and he allows her to go ‘checkmate.’”

Why guests didn't fight? It sure would seem better to try than die by immolation.

“From Chef Slowik’s point of view, they’re not getting their comeuppance, they’re getting liberation, they’re getting rebirth,” Mylod explains. At least in the mind of the chef and his minions, this is about cleansing the elite of their sins. And while not all of them are as fawning as Margot’s date to the festivity, Tyler (Nicholas Hoult), they’re all susceptible to being brought in by Chef’s cult of personality.

“The absolute futility of escape coupled with the journey they’ve been on, that whisper in the air of Slowik’s words over that evening, over the dinner, the combination of those two elements is just taking them to a place of absolute naked submission,” the director adds.

Notes:

And also what's wrong with staff, were they really that brainwashed commited to menu experience willing to sacrifice their own lives? It doesn't seem realistic at least some would not change their mind in the very end seeing death as irreversible consequence.

You could compare it with what goes on in a cult. The staff worship chef Slowik as their lord and savior, and they live and die only to serve him.

Male diners get the chance to escape, but fail.

The cheeseburger looked really scrumptious , better than the other dishes.

45 seconds head start is hardly a chance to escape.

@Markoff said:

45 seconds head start is hardly a chance to escape.

At least they tried. Tyler seemed a bit reluctant to flee. Of course in the end there was no escape.

@wonder2wonder said:

Director Mark Mylod has given some answers in this article. Below are his quotes. For more details and possible answers to your other questions, you can read the complete article.

@Markoff said:

He said she is just eater/taker and then thanks to nostalgia (?) he changed opinion just because she ordered something (burger) he liked to prepare to go? It doesn't really make sense.

“Ralph’s character and Anya’s character are about connection,” Mylod tells us. “Ultimately, she has manipulated him. He also realized that she’s manipulating him but he allows her to win. All the unspoken business is in the final discourse between them and the burger. It’s a mutual understanding… and he allows her to go ‘checkmate.’”

Why guests didn't fight? It sure would seem better to try than die by immolation.

“From Chef Slowik’s point of view, they’re not getting their comeuppance, they’re getting liberation, they’re getting rebirth,” Mylod explains. At least in the mind of the chef and his minions, this is about cleansing the elite of their sins. And while not all of them are as fawning as Margot’s date to the festivity, Tyler (Nicholas Hoult), they’re all susceptible to being brought in by Chef’s cult of personality.

“The absolute futility of escape coupled with the journey they’ve been on, that whisper in the air of Slowik’s words over that evening, over the dinner, the combination of those two elements is just taking them to a place of absolute naked submission,” the director adds.

Notes:

And also what's wrong with staff, were they really that brainwashed commited to menu experience willing to sacrifice their own lives? It doesn't seem realistic at least some would not change their mind in the very end seeing death as irreversible consequence.

You could compare it with what goes on in a cult. The staff worship chef Slowik as their lord and savior, and they live and die only to serve him.

Male diners get the chance to escape, but fail.

The cheeseburger looked really scrumptious , better than the other dishes.

Replace the sesame seed bun with an onion bun & I would wholeheartedly agree!

Chef was jaded with the life he (willingly or unwillingly) got pigeonholed into. You see when Anya is looking at his old photos - how miserable he looks in most of them where he is a professional, and the only one he is happy in was when he was employee of the month as a bugger flipper. She played this nostalgia card on him, and I think for the first time in many years he enjoyed cooking again. Because she had sparked that feeling in him again he felt she did not deserve to be with the rest of them - them meaning those who had truly lost all taste for life.

Obviously this movie seems to be an allegory, the guests and the restaurant are more symbols and not a realistic situation. I mean, his home's floor plan is built exactly as his restaurant, it's right there on the nose. So I would not try to reflect realistic behavior and intentions on the characters, it's very much not the point of the movie.

He let her go because she took herself outside of the equation, by showing independence and individuality she then didn't belong with neither class. He didn't see her as being part of the menu anymore, not part of the experience he conducted.

Nice movie, I would say it's dealing with the same themes as Parasite and Triangle of Sadness are.