The meaning behind “Major Bag Alert” is quite simple: It’s an indication of having a lot of money. Indeed, the term “bag” (lots of money) and versions of it (“spending a bag,” “blowing a bag,” dropping a bag,” etc.) have long been used in hip-hop. By saying “Major Bag Alert,” it’s alerting others that a serious amount of cash has been or is about to be amassed or spent. It could also be used to describe an individual who wants to come off as being affluent, letting others know that they have a “major bag.”
TikTokers have been using the phrase and audio to humorously describe situations that involve making tons of money. For example, user @bethannrobinson joked that her long distance relationship would be a “major bag alert” for Delta airlines since she spends so much money on plane tickets to visit her boo.
Source: https://www.distractify.com/p/what-does-major-bag-alert-mean