Word of mouth. Make things that work well, people want, and stand out - and they will spread by themselves. I block 100% of advertising on all platforms I use, yet somehow never have difficulty finding things when I want to find them. And that often includes stuff from very small providers. Search + reviews, and so on are a million times more useful than advertising. And getting a hundred or so early users/testers/etc to seed those reviews/etc is trivial in modern digital times.

The world itself would almost certainly be a much better place without large scale/centralized advertising. I think the argument about it providing product discovery for hidden gems is nonsense. In reality it's mostly just crap, artificial demand creation, and behemoths trying to maintain brand image.

Usually brands collaborate with influencers on tiktok, instagram, facebook, youtube.

I’ve found that younger users tend to instinctively swipe away from flashy interstitial ads on tiktok/reels, but are far more likely to be engaged by a talking head influencer reading the same script.

When you advertise via parasocial word-of-mouth, you don’t even need to link your app in the post, as users are likely to take the time/effort to search for your app on the app store.

Unfortunately, the ad platforms/exchanges don’t really profit from these types of brand/influencer collabs.

The general problem of how to advertise a small business has never been solved.

I see ads for some local pizza places, as they've learned that can work for a delivery business, but most restaurants have no ads. They don't know of anything that works.

Influencers sometimes have very niche / local audiences

The standard advice I've always read: Get active in the niche for your app/game, be it a subreddit, a discord, tiktok or whatever.