[noun] + は/も + 少なくない [verb plain] + ことは/のは + 少なくない [noun] + が + 少なくない
Note: 少なくない is the negative form of the い-adjective 少ない (少ない → 少なく + ない). Functions as a predicate meaning "not few / quite a lot."
すくなくない (すくなくない少なくない) is the negative form of the い-adjective すくない少ない (few, little). It literally means "not few" or "not a little," and is used to express that something exists in a considerable amount – equivalent to "quite a few," "quite a lot," or "not insignificant" in English.
This is a form of litotes – expressing something positive through double negation. Rather than directly saying おおい多い (many), using すくなくない少なくない sounds more measured and objective, which makes it common in written language, news, essays, and formal speech.
While おおい多い is a direct statement that something is "many," すくなくない少なくない carries the nuance of "more than you might expect" or "a significant number." It often implies that something is noteworthy or should not be overlooked.
It can also be conjugated into the past tense (すくなくなかった少なくなかった) or the polite form (すくなくないです少なくないです / すくなく少なくありません).