is there a sensible way to gain instagram follower?

Pick a lane and stick to it. Accounts that post about one thing grow faster than ones that post about everything, because people follow for a reason. Reels are still the main way new people find you, so get to the point in the first second or two, and do collab posts with accounts your size - you show up on both profiles. Don't buy followers, it tanks your engagement rate and the algorithm reads that as nobody caring.