Fediverse

If you want Instagram users to move, there's no real alternative to Pixelfed. You can literally move an entire account full of images and posts over from Instagram to Pixelfed.

If, however, you're seriously eyeing Bonfire, check Hubzilla. Bonfire promises lots of stuff. Hubzilla offers more than what Bonfire even only promises and then some. Also, while Bonfire is still in fairly early development, Hubzilla is tried-and-true, stable software that has been in development since 2012, for even longer than Mastodon. And Hubzilla only needs a LAMP stack. Basically, Bonfire is Hubzilla from Wish.com at best. And AFAIK, Hubzilla even needs fewer server resources per user than Friendica.

Downsides: There's no phone app (but then, there's none for Bonfire either). You've got no other choice but to use the Web interface; at least Hubzilla can be installed on phones as a Progressive Web App. On top of that, especially the default theme is not really user-friendly and kind of stuck in the early 2010s, and for alternative themes, you need to include third-party repositories into your installation. Posting images isn't as straight-forward as on typical social media; it's more like a blog in the sense of having to upload image files before you can use them. And if you want alt-texts, you have to learn to get your hands dirty on BBcode.