I now have black borders around my YouTube video. I don't know why or how to correct it.

I have been using elements 2021 for some time.  I upload my video to my YouTube channel, Boonie Buster,.  All of my previous videos have appeared without black borders.  About 5 months ago I started getting the black border.  To my knowledge, I have not made any changes to my cameras or the Elements program.  You can view my channel and see that it started, even with the Thumbnails, about five months ago.  I have been ready other responses and doing some research on the web, but I can not figure out how to correct this.  Any help would be appreciated.  My YouTube channel is linked below. My cameras are an Android cellphone, a DJI Pocket camera, and an occasional GoPro camera.

https://www.youtube.com/channel/UCPhkhEKztDWWlaGVOy7qUiQ/videos