B1 unconvincing about China according to Macron (7)
I believe the answer is:
thiamin
'china according to macron' is the definition.
I can't judge whether this defines the answer.
'b1 unconvincing about' is the wordplay.
'bi' becomes 'iam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'unconvincing' becomes 'thin' (I've seen this before).
'about' indicates putting letters inside.
'iam' inserted inside 'thin' is 'THIAMIN'.
Can you help me to learn more?
(Other definitions for thiamin that I've seen before include "Vitamin in cereals, beans, etc" , "food ingredient" , "Vitamin B 1" , "Essential nutrition" , "vitamin required" .)