Some of the installed man pages require an update. For example strlen.3 printf.3
have a look at https://man7.org/linux/man-pages/man3/strlen.3.html

from man7.org:
The strlen() function returns the number of bytes in the string pointed to by s.
...
Linux man-pages 6.04           2023-03-30

from man 3 strlen:
The strlen() function returns the number of characters in the string pointed to by s.
...
This page is part of release 4.16 of the Linux man-pages project.

info libc is more up tp date.

For example strlen( "öäü") returns 6.

An update of man-pages would be nice.
Greetings.