iTunes used to be able to do this but I’m not sure now. Here’s an excerpt from iMazing.
———
Download and install iMazing connect the source device and from the right pane select
Manage Apps > Library (top left toggle) > select the old app > Download to Library ...
Then connect the target device select Manage Apps > Library > Install ... and you're done.
All this is free, no registration or purchase necessary.
More details here:
https://imazing.com/guides/how-to-manage-apps-without-itunes
———
For Qardio, you don’t have to worry about accidentally updating it and lose functionality because it’s gone from the App Store. But others apps that still exist on the App Store but may have features removed in an update, make sure you refrain from updating those particular apps.
Can you use someone else’s app? Maybe.