First of all, Qt Creator doesn't seem to have an option to save files with UTF-8 Encoding.
However, if one wants to put Unicode characters inside a string, it would be a nice-to-have feature.

If I save my file with UTF-8 encoding with another text editor and later open it with Qt Creator, it shows mismatching characters instead of the Unicode characters.

For example, my last name "Kristóf" reads as "KristĂłf" when opened in Qt Creator, although it appears in my application correctly when I run it.
Note that the issue appears both when I save the file using "UTF-8 with signature" and "UTF-8 without signature".