I'd recommend using paid ads to get to get inital users. It provides the easiest and fastest feedback loop. They don't need to be profitable think of it as paying for real beta testers.
Depending on your niche organic tiktok can be good. SEO can be good longterm if you have a landing page/website that explains your app, you can also make demo pages and tool pages that relate to your apps niche.
Submit your app to any directories that it fits into.
Organic social media is always good just try and make sure the content/app provides real value to the users dont just spam post boring ads else they will get no views.
