Upset, unfortunately, about Strictly's opening dance (5)
I believe the answer is:
salsa
'opening dance' is the definition.
'salsa' can be an answer for 'dance' (type of dance). I am not sure about the 'opening' bit.
'upset unfortunately about strictly's' is the wordplay.
'upset' says the letters should be written backwards.
'unfortunately' becomes 'alas' ('alas' is used to express regret).
'about' means one lot of letters goes inside another.
'strictly' becomes 's' (this could be a standard abbreviation which I don't know about).
'alas' placed around 's' is 'aslas'.
'aslas' back-to-front is 'SALSA'.
Can you help me to learn more?
(Other definitions for salsa that I've seen before include "dressing" , "Hot dance - hot sauce" , "Spicy tomato sauce" , "This could be hot" , "Steps" .)