It is common to cut-off the sides to reformat into a tall/vertical video that fills (or nearly) the 9:16 frame. You are not supposed to put a wide, landscape into a short/reel. Scroll down the page for the link you shared. Most of them are full vertical videos.
Honestly, for that video, you might want to think about making a new video project in a 9:16 vertical aspect ratio and position things accordingly for that. Otherwise, the platforms are going to demote your video.
Knowing what Video Mode you need before you start is vitally crucial, and often misunderstood. Once the Video Mode is set, there is no need to enter into Export → Advanced unless you know what you are doing.
Guessing from your very first post, a vertical Video Mode is needed.
Most likely, you’ll need to start a new project from that vertical Video Mode.