Have you considered using a podcast player which can play local files?

They are specifically built with annotations and notes and should help better in this regard. I can’t give specific recommendation but you can find a good one on fdroid by searching and using some.

Android has added app archival feature for app stores starting with Android 15. Currently unobtanium does not do it since the developer has not implemented the api and necessary features to support it.

Check the difference on other phones. Try different file manager apps to see which can do the task faster. Try turning on battery saver mode – sometimes background processes can slow foreground apps.

To be consistent test 3 times in flight mode. Also, when your phone is warn/hot it can slow down drastically compared to when its cold to the touch.

UFS 3.1 is not necessarily bottleneck here. It also depends on the optimization by OEM.

According to this youtuber some brands UFS 2.2 storage outperforms UFS 3.1 storage used by other brands solely due to their software optimization. Skip the video to 04:54s to see the zip uncompression test and a few mins back to see the results of other tests.

https://youtu.be/mOm4RbC5qxc

Can you share a test file so we can compare the results and rule out a bottleneck with your device?

You absolutely can.