What is the meaning of the Datthabba Sutta?
MN1 states:

MN1:171.4: ‘Nandī dukkhassa mūlan’ti—

The happiness of nibbana is therefore empty of nandī.
MN1 also states the difficulty of this understanding:

MN1:172-194.31: But the mendicants were not happy with what the Buddha said.

Perhaps the clarification here may help, since there is identification in nandī:

MN1:148-170.24: nibbānaṁ nibbānato abhiññāya nibbānaṁ na maññati, nibbānasmiṁ na maññati, nibbānato na maññati, nibbānaṁ meti na m
aññati, nibbānaṁ nābhinandati.

MN1:148-170.24: But he doesn’t identify with extinguishment, he doesn’t identify regarding extinguishment, he doesn’t identify as
extinguishment, he doesn’t identify that ‘extinguishment is mine’, he doesn’t take pleasure in extinguishment.