I am now not trying to get in the way of your getting your new post out, but when you have time to get into this, DN 15 Chapter 4. Attasamanupassanā (despite that sub-title) is largely about Feelings (and its connection or otherwise to ‘a self’)
Taking also other sutta and the posts into account, it is taking the feelings to be the self (I am ‘this’ or ‘that’ feeling’) that is not acceptable. Because feelings are fleeting, impermanent.
Towards the very end we find in this (DN 15) sutta:
“Now, as to those who say:
‘Feeling is definitely not my self. But it’s not that my self does not experience feeling. My self feels, for my self is liable to feel.’
You should say this to them,
‘Suppose feelings were to totally and utterly cease without anything left over.
When there’s no feeling at all, with the cessation of feeling, would the thought “I am this” occur there?’”
“That’s why it’s not acceptable to regard self as that which is liable to feel”.
Yet, going by MN 59, there appears nothing wrong with holding that feeling is there, as a factor of or ‘accompanying’ happiness, ‘wherever it’s found, and in whatever context’,as long as it is not taken as one’s Self. And as with an Arahant the sense of self (asmi mana) is not there anymore to start with, there cannot be taking it (feeling) to be ‘his’ self… where there is no self in the first place, that is. All others below the Arahant will have a sense of self and may therefore ‘attach’, feeling or sanna or vinnana or sankahara, to that self.
That is what I have been able to make out this far.