Why can't I add music to my Instagram feed post? Everyone else can.

Usually one of two things. First, music on feed photo posts rolls out by region and account type, and business/creator accounts in some countries get a limited or licensed-only library for rights reasons, switching to a personal account sometimes restores the full one. Second, make sure the app is fully updated, this feature has been buggy and often just needs the latest version. It's genuinely not you, it's Instagram's licensing patchwork.

Not cursed, just geoblocked by music lawyers. The most Instagram problem there is.