why iphone does not support rar media files? when i extract video file it does not open it

The iPhone supports only a limited number of video formats. If the file is one of those you should be able to view it with the TV app. If it doesn’t appear in the TV App you will have to convert it on a computer or download an app from the App Store that can play that format.

“i know but when some body whatsapp me media file in archive format“

Ask them to send you the original file and NOT in an archive format.

rar is an archive format, it is not a video format.