Usually I use MS Word to edit my books and then I upload them to Calibre, convert them to ePub and finally convert the ePub to Kfx format.
I noticed that the popup footnotes takes the whole screen when I use this procedure, even though the footnote is a single line
I tried converting an epub file from the internet (not converted from MS Word via calibre) and the footnotes worked perfectly.
When I convert from MS Word using calibre:
When I tried the internet file:
I attached both epub files for the internet version and the converted version down below: