iOS has Safari Services for when an app wants to support visiting a 3rd party site (so you don't want a WebView) without leaving the app.:
https://images.squarespace-cdn.com/content/v1/52428a0ae4b0c4...
As you can see a clear "Done" button, that's straightforward enough. Hit it and you go back to the app.
But even better, you can promote it to a normal browser tab by hitting the Safari button at the bottom!
That will transfer the tab to Safari with a transition to make it clear now you are in Safari can use the app switcher to go back and forth.
It's a great example of how the SDK baking explicit back handling into components ends up being better than a generic "always goes back" concept apps have to implement.
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Ironically Android has something similar called Custom Tabs but they're not widely used for multiple reasons: https://medium.com/@vardaansh1/use-chrome-custom-tabs-they-s...
I'm also not sure if they support promotion to a browser tab natively, I'm guessing you have to add your own UI to close it and fire off an intent for the system browser