How do you make a square Shorts video?

Today I tried uploading videos in different resolutions to get a 1:1 format. I think those who watch Shorts on a computer or TV have noticed that some Shorts have a non-standard resolution. But when I try to set 1:1 in CapCut, or manually make it 1080x1080, YouTube automatically adds black bars. How can I upload a video without these bars in a wide square format?