The fact that you didn't mention Threads speaks volumes.
But what you need is desktop accessibility (which Threads doesn't have. Instagram is a mobile-first picture-focused app, and doesn't need it. but I'd much rather type on a keyboard than use my phone), and a giant pile of money, from which you pay people to post content exclusively to your app (which Threads hasn't done). From there, you get influencers to pump out screenshots on the existing apps, making it seem like the conversation is happening there and that they're missing out by not being on your platform. Finally, in order for people to want to use it, there needs to be some sort of a new hook. You can't do E2E encryption because Signal did that so it's table stakes at this point. It can't be auto-deleting and no screenshotting because Snapchat already did that one. And so on.
But what you need is desktop accessibility (which Threads doesn't have. Instagram is a mobile-first picture-focused app, and doesn't need it. but I'd much rather type on a keyboard than use my phone), and a giant pile of money, from which you pay people to post content exclusively to your app (which Threads hasn't done). From there, you get influencers to pump out screenshots on the existing apps, making it seem like the conversation is happening there and that they're missing out by not being on your platform. Finally, in order for people to want to use it, there needs to be some sort of a new hook. You can't do E2E encryption because Signal did that so it's table stakes at this point. It can't be auto-deleting and no screenshotting because Snapchat already did that one. And so on.
It's an interesting problem!