For comparison:
https://pubs.opengroup.org/onlinepubs/9699919799/

In an utf8 environment the number of bytes written may differ
from the number of characters.

Example:
fprintf( stdout, "%*s\n", fprintf( stdout, "öäüÖÄÜßµł€\n"), "^");

From https://man7.org/linux/man-pages/man3/dprintf.3.html:
"Upon successful return, these functions return the number of
 characters printed (excluding the null byte used to end output to
 strings)."

Greetings.