Why can’t I see the repost button on an Instagram post or Reel?

The built-in repost control is meant for public Reels and feed posts, so it won't be there for content that isn't public. Update Instagram, reopen it, and try a couple of different public posts or Reels in the mobile app. If it’s missing everywhere after that, there isn’t a dependable account setting that forces it on—use a Story share or DM for now instead of handing your login to a third-party repost app.