Wait a second, I play among us on mobile and have not encountered a single ad. Why? I haven't modified the game in any way.
Oh, yeah, I remember ! They recently removed ads for a time because some people were getting unappropriate ads. They will enable them again some day, but until then, there are no ads on mobile.
Although, some people say they never got ads since the game released in 2018. There are reports that the ads sometimes never trigger.