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means something that is not an inconsequential matter, not a trifling thing.
Definition from the Cambridge Academic Content Dictionary
something that deserves serious attention, especially an amount of money:
"An extra two thousand bucks a year is nothing to sneeze at.
The Word Detective says;
“To sneeze at” something or someone is a colloquial usage, first appearing in the early 19th century, meaning “to regard as of little worth; to disparage, disregard or despise” (“It's a sort of thing a young fellow of my expectations ought to sneeze at,” 1806).