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.
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.