Yes, it is a fragment, it's not a sentence. It could be a sentence without the word although. "I finished." is a sentence. Using the word "although" needs a sentence that the word is referring to either in front of it or after it.
Although I finished, I was not happy with the work.
I'm still hungry, although I finished my lunch.
You should not capitalize a sentence fragment following a colon.
A group of words that cannot stand alone as a sentence
It is a subordinate clause.
Combine it with another sentence.
My best regards,
It is true
Do you work? is a complete sentence; it is not a sentence fragment.
"She wave." is fragment but "She waves" is a sentence.
fragment
It is a subordinate clause
Fragment.
sentence fragment