Hi @ericonline ,
Have you installed the PowerApps Mobile App within your iOS device?
Do you want to open a canvas app within PowerApps Mobile App in your iOS device via clicking the App URL?
If you want to open a canvas app within PowerApps Mobile App in your iOS device via clicking the App URL, I afraid that there is no way to achieve your needs in PowerApps currently.
If you would like this feature to be added in PowerApps, please submit an idea to PowerApps Ideas Forum:
https://powerusers.microsoft.com/t5/PowerApps-Ideas/idb-p/PowerAppsIdeas
In default, when you click the App URL in your Mobile device, it would open a web page in browser in your Mobile device rather than open the specific app using PowerApps Mobile App.
In additon, based on the message that you mentioned, it means that your canvas app are using some features/funcationalities are not supported within browser in Mobile deivce. Please consider open your app using PowerApps Mobile App directly, rather than open the app via clicking the App URL.
Best regards,