What is typical growth for a bootstrapped app with no existing brand presence

I think there is a huge variance. Some (probably most, tbh) apps see no traction at all, some grow slowly, some take off. But the takeoff can also happen after a long period of slow growth/stagnation, depending on influencers covering it, word-of-mouth, etc. The market is flooded with apps, so you need to think about what you can build that is worth choosing over all of the other options which already exist.

I'm in the same boat so i would love to know the answer to this as well

Competition is high. In my opinion, 6 months to 1 year is a realistic period, but it all depends on marketing and outreach.

i'd say it takes at least a year, even with paid marketing, to retain a stable growth. my other product took 1year and 7months.

I've had a weird launch, got more people to try the TestFlight (Beta) for the app than real downloads at the launch... Now growing slowly, about 5 users a week, with decent ASO rankings & 0 paid marketing. Plans to change that of course!