Please tell us some basic information before asking for help:
Model Name: Asus 6z (IN)
Rooted or not: not
Frequency of Occurrence: every time
APP Name & APP Version (If your issue relates to the app): stock gallery app and google photos after the android 11 update
I captured video on 480fps after that i went to gallery to play it, It plays like a fps drop video, after i save(trim) the particular part with slow mo via exporting method ( like there is an option for particular part of the video plays in slow of 480fps by save option at right side top corner) after exporting the video plays smoothly without any fps drop,
I also tried to clear the cache for gallery app and reboot the phone but no use.
I think this is small bug, 240 and 120fps was playing fine but while playing 480fps was not smooth, even old files also getting same problem i attached a sample video for your reference