Thats a Maxx air fan and those are the factory mounting tabs for a cover. They are for
THIS specific cover.
Here is the kicker. If they did not get sealant under those tabs when the fan was installed they can leak. If you look you'll notice that they are open inside the tab to the underside of the mounting flange.
What you'll also find is that due to the sidewall being so thick on that specific fan, the brackets provided with other brands of covers, and even some of Maxxairs like the Maxxair 2 will be too long if trying to mount them per the instructions with screws into the opening sidewall.