Try the Busuu, Nextlingua, Babbel, Pimsleur,... app if the same happens.
Do you have animations and motivational messages all deactivated?
Sometimes it is on Duolingo a strange combination of various specific app versions vs latest OS vs Beta version vs a specific phone hardware.
Duolingo developers can't test all possible scenarios and "too new" is most of the time not a good thing (Beta OS).
So how "new" is that IOS version and phone hardware? Quite new, right?
Sorry, I'm not an Apple user.
Those reports have risen before on the Duolingo community discussion forums so it's not something very new we know about.
How healthy is the lipo? Can you launch an app like Droid (Android) which reads out some info and sensor temperature states?
My Xiaomi Miui actively kills inactive apps from the foreground (Battery saver).
Duo has implemented a caching method which means it downloads 1.68Gb of user (old tree) data.
But that download runs on Android over night so I had to allow background processes and exclude Duolingo app from MIUI's battery saver.
Much older Android app from April 2022 doesn't run hot here, not even when actively using it for several minutes.
It could be an issue or maybe something else is using a lot of Cpu and Gpu power?
Have you restarted the phone yet?
Sometimes newest store app versions are buggier than older versions.
But hard to tell which bug is contained in what version.
How can you do an app version downgrade on Apple IOS?
History files from 6-12 months ago?
Manually installing an archive file?
Do you have an older BACKUP (complete phone backup or app/data backup) which you might be able to restore for more tests?
Is this even supported on IOS?
Manually installing an older app version from a (trusted) archive site is the way to go on the Android platform.
I expect it works very differently on IOS.
Android Google Play store does NOT support selecting an older version from HISTORY for install.