HRT treatment remains open to debate (6,3)

I believe the answer is:

thrash out

'debate' is the definition.
(I've seen this before)

'hrt treatment remains open' is the wordplay.
'treatment' indicates anagramming the letters (letters treated or processed differently).
'remains' becomes 'ash' (remains of a fire).
'open' becomes 'out' (I've seen this in other clues).
'hrt' is an anagram of 'thr'.
'thr'+'ash'+'out'='THRASH OUT'

'to' is the link.

(Another definition for thrash out that I've seen is " Debate".)

I've seen this clue in The Guardian.

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