Specs good enough for simple app?

Is it good enough?

Probably not.

To submit to the App Store you need to use Xcode 15 [1]. Xcode 15 requires macOS 13.5. AFAIK 2011-era MacBooks top out at macOS 10.13.x.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Well, not yet, but the App Store has announced that they’ll required this as Apr 2024.

What Quinn said about publishing on the App Store (but may be you don't want to publish ?). If you just want to install the app from the Mac to the iPhone, you need to check the compatibility (an old Xcode will not generate for recent iPhones).

However, old Mac will not let you install recent MacOS and thus not install recent Xcode.

With macOS 10.13, you would have to install Xcode 10.1, which is very old. It is not impossible, but that will make your development harder (for instance when you search for help on the web, you will get proposals that you cannot implement).

So all in all, 2011 Mac is a risky try. You may end up developing an app (it is possible of course, even on a 2011 Mac with an older Xcode), but never be able to load on the iPhone.