Some videos on my camera roll dont have sound

Pausing the download which was syncing solved the issue. Great solve, thanks!!!

I can only think of two possibilities for the issue of the greyed-out speaker icon.

1. Do you have enabled iCloud Photos and your device is not connected to the internet? if you have recently enabled iCloud Photos and the syncing process is ongoing while you are viewing videos in the Photos app, it's possible that the lack of internet connection could interrupt the syncing process and potentially lead to inconsistencies in displaying the audio status of the videos. In such cases, the speaker icon may appear grayed out until the syncing process is completed for all the videos or a stable internet connection is established.
2. Probably these videos were imported or synced to this iPhone from another device. In that case, your videos may have an Audio codec compatibility issue. Certain video files may have audio codecs that are not supported by the iPhone. In such cases, the video will play without sound, and the speaker icon may appear grayed out. Ensure that the videos you are playing have compatible audio codecs, such as AAC or MP3, for the best compatibility.