NOMO. I'm a photographer by career and own way too many cameras - Sony A7rIII, Sony A7sII, Fuji XPro2, Panasonic GH5, you name it - I'm always the most excited to see what my shots look like with NOMO, especially when they're Portrait mode shots processed through the app. It's $20 for the full deal, but I personally think the iPhone (expecially the XS/XR with the dynamic range) is better suited to simulating fun disposable camera-style film snaps than it is trying to replicate a DSLR/mirrorless, and I'm constantly surprised at the results. Sure, I could do this stuff myself with a mix of Lightroom and maybe Photoshop to get the overlays, but the iPhone as a camera should be about speed and this keeps it quick.
These shots I took are all iPhone XS Max, a mix of regular quick snaps and Portrait mode shots, all run through various NOMO cameras. With the $20 purchase it allows you to take photos in any app (stock for portrait mode, for example) and then process the finished photos through the "camera" of your choice.
Here's a taste, but more in the gallery at the link below the picture.
https://imgur.com/a/RANL5w8