I've tried creating an iOS app using natively.dev.  While I believe it did create an application that would build, it wasn't functional because if issues with the integration between either the expo.dev website, or the way it was attempting to pull down images and videos.  
I will likely need an Apple Developer account to get this to work, but it might be worth a try.  $99 to maybe build an app that my wife would use.  
Birthday present, for ... me ... and her?
Unless I can find a way to sideload the app onto my phone to begin troubleshooting it, this will probably die here. I may bring the code into xcode and see if I can run it there, and if it will work to troubleshoot it? If I can get it working in a simulated phone, it may be worth spending the money on getting the dev account. If the app is popular, and I sell it for something like $0.99, I can maybe make up my Apple Developer costs, or enough of them to make it worth while. If I make it free, and maybe include ads, with a $0.99 life time ad-free option ... that could work. Hard to say. There are a lot of very fancy slideshow apps out there. I'm really just wanting a very basic one that doesn't have annoying watermark or $5+/mo subscirptions fees to just do more than 50 pictures (you know who you are).
Well, we'll see.