In the editor mode, the footnote number appears as a superscripted number. But in preview mode, it appears at the same level as the alphabets. I checked Obsidian help files. The demo they have given there, the footnote appears properly superscripted even in preview mode.
Well, I’m not sure if you just didn’t mention it. But when I test this, it doesn’t make it superscripted until after you have a corresponding footnote. As soon as I add the footnote, it superscripts for me.
If you do have a foot note, and just didn’t mention it, could you show a screenshot or something? And test it in the Help vault with no plugins, just in case.