Once you download the app, head back to your old iPhone and try downloading it from your Purchased list, following the same steps as in the previous method.
The key is to make sure you log into your iCloud account on the newer device to ensure that the app is saved to your history of app purchases.
When you do, the App Store will display a message asking if you want to download an older version of the app. You can ignore that message and proceed to hit the download button anyway. On the app page, it's common to come across a message telling you that an app Requires iOS 13.0 or later, leading you to believe that your phone is incompatible. That's because the App Store doesn't clarify whether an older version of an app exists. This is the easiest option available to download an older version of an app, but one that you may not know about. Let Apple Download the Last Compatible Version
