"Photos cannot play this video because the resource is unavailable" how to fix?

Can you tell us more about your setup? There might be several possible reasons for videos not playing.

• What is the format of the videos that cannot be played? Are the videos QuickTime videos or AVI? QuickTime and AVI are container formats that might be referencing the video component outside the actual video. If you moved the videos to a different disk, the video component might have been left behind. Then you have to find the original volume with the videos.

• Which system version do you have installed? If you are now running Catalina on your Mac, some video formats are no longer supported and need converting to a supported format.
• And where is your Photos Library stored? Is it on your system volume or on an external volume? Photos may not be able to play the videos, if the Photos Library is on a volume with a different file system format from your Mac, for example, if the file system format is case-sensitive.
• Is iCloud Photos enabled for your Photos Library? Then the videos may still need downloading from iCloud.

There are several possible reasons,

I am asking,