I use the phrase insight of for the sentence "It gives me an insight of what college life should like." but Grammarly change it into "an insight into". Under which content we use them?
Beware of Grammarly and other sites providing software that purports to give advice on how to write English. Grammarly provides no credentials for its staff and purports to be AI driven, a technique that fails to capture the complexity of English idiom.
The Corpora of Contemporary American English finds 46 prepositions that can follow the word insight. Note that the preposition into contributes 75% of the text examples. This is actually an underestimate since what we're really talking about is a preposition that introduces the area illuminated by the insight. The preposition of, for instance, usually reports who has had the insight:
The insight of the researchers into the mechanism of the chemical interactions.
But not always. See example 8 below, from the following list.
 By reminding us that the [Republican P]arty was not always broken, such a history might offer some insight on how to make repairs. (New York Times, 1/4/15)
 Longer follow up data in Syrian refugees will provide more insight in the outcome of these patients. (Kidney Blood Pressure Research, 3/1/19)
 [S]everal businesses that worked on the reservation before moving their operation over to the WMSP [White Mountain Stewardship Project] provided insight to the Tribe's contributions. (Journal of Forestry, Vol. 115, Iss. 6, Nov 2017)
 Sylvia Plath gave mental illness an aura of nonconformity, creativity, and even acute insight about social and political affairs. (Journal of American Culture, March 2014, Vol 37, Issue 1)
 Those models may provide insight regarding quantitative changes one might expect on multiple time scales. (Physics Today, 2011)
 Analyzing this pre-post measure provides valuable insight concerning the state-of-mind of the individual prior to entering the student experience (Education, Vol 114, Issue 2, Winter 1993)
 Educators who value the input from parents providing unique insight toward their children will likely be able to create effective programs.... (Education, Vol 127 Issue 1, Fall 2006)
 In order to gain full insight of the informant's perspective and understanding of the course, his journals, midterm examinations, and term papers were examined. (Journal of Instructional Psychology, Vol 41 Issue 1-4, 2014)