The most common and most likely answer to this crossword clue is the 6 letter word BLITHE
I've seen this crossword clue in The Guardian
B
L
I
T
H
E
More clues leading to the result BLITHE
- Carefree bachelor having much flexibility
- Heading for ball, supple and cheerful
- Beethoven’s first, graceful and gay
- Student in scrap with man is completely unconcerned
- Untroubled when article on British life’s half missing
- Happy and carefree as a Round the World sailor, say
- Happy to prattle endlessly
- Bishop’s settled and he’s happy
- Happy, born flexible
- Coward’s spirit is kindled by British hero? Not half!
Buddy explains!

The straight part
We know that "Untroubled" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case untroubled = blithe.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BLITHE mean?
BLITHE adjective- (dated or literary) Happy, cheerful.
- Casually indifferent, careless, showing a lack of concern.