I was flying with my Mavic 3 , and noticed when I went to move the files that all the media wasn’t in the 100 media file where it usually is and some was in a new file titled 101 media. I didn’t create 101 media it just appeared. Anyone know the reason for this

That's how digital cameras work.
When you get to DJI_0999 (as high as DJI file numbering goes), the camera makes a new directory called 101 Media.
If you shot another 999 images on the same card, the drone would open 102 Media etc, etc.
This prevents files overwriting older files with the same filename.

Hello there. Good day and thank you for reaching out. Kindly please refer to the post given above by Labroides on post #2 for reference on this matter. Thank you and have a nice day.