Pixelfed is the federated alternative to Instagram photos and clips. Loops is another one, more centered around video clips. I have no idea if they have porn but I would imagine so.
Upscrolled isn't USA-based and not good for much but it does have a surplus of the type of content you're interested in. It was touted as the anti-corpo Instagram but it's just another manipulated and poorly handled social app that luckily for you, has a ton of porn.