The most common and most likely answer to this crossword clue is the 10 letter word CORONATION
I've seen this crossword clue in The Guardian
C
O
R
O
N
A
T
I
O
N
More clues leading to the result CORONATION
- My old folk in exalted ceremony
- Choirboy oddly selected to lead country for royal event
- Commanding officer helping guards working in ceremony
- Bill’s partner welcoming king before state ceremony
- I’m amazed by old people’s investment
- Enthronement of firm king’s naught to the country
- Ceremony, for my people embracing love
- Royal ceremony sans technology returns after pandemic
- Company allowance should cover close to ceremony
Buddy explains!

The straight part
We know that "investment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case investment = coronation.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 CORONATION mean?
CORONATION noun- The act or solemnity of crowning a sovereign; the act of investing a prince with the insignia of royalty, on his succeeding to the sovereignty.
- A success in the face of little or no opposition.