The research on it is pretty murky because marketing firms frequently fund research studies but if you poke around at some of the many meta-analysis papers out there I think it’s hard to conclude that advertising is a net profit for big companies, at least in a dollars in dollars out sense. Freakonomics did an interesting episode on the topic in 2020.

For a new brand with zero visibility I’m sure ads gain new customers, but established brands (which make up most of the advertising I see) probably aren’t making much of an impact on their sales with their incessant campaigns.