My personal definition of an influencer is anyone who has the ability to get their following to follow and want to buy from a brand just by advertising the brand. Imo follower counts aren’t as important as their ability to, well, influence their followers to buy. I’ve seen people with as low as 5000 followers get brand partnerships just because their followers responded well to their ads. Of course, people with larger followings are always more desired than people with smaller followings because the brand reaches a larger audience, and even if only a small percentage of their following buys, that’s still a lot of people.
As for becoming an influencer, it’s all about marketing yourself. Keeping your posts consistent is super important. Pick one or two related topics (such as makeup & fashion or fitness & healthy recipes), find an aesthetic that you like and will keep for a while, and create a consistent posting schedule. This alone can help boost your organic growth, but don’t count on your content alone carrying your account. Interaction with your followers and other people who post similar content is very important too and can help you grow your connections and keep your followers loyal. It’s all about very careful marketing.