Specify which documentation you found a problem with
Doc for CURLMOPT_PIPELINING option.
https://curl.se/libcurl/c/CURLMOPT_PIPELINING.html
The problem
Doc https://curl.se/libcurl/c/CURLMOPT_PIPELINING.html says that CURLPIPE_NOTHING is Default, which means doing no attempts at multiplexing. So it sounds like this value is used by default, but CURLPIPE_MULTIPLEX is specified in the section Default.

Specify which documentation you found a problem with
Doc for
CURLMOPT_PIPELININGoption.https://curl.se/libcurl/c/CURLMOPT_PIPELINING.html
The problem
Doc https://curl.se/libcurl/c/CURLMOPT_PIPELINING.html says that
CURLPIPE_NOTHINGisDefault, which means doing no attempts at multiplexing. So it sounds like this value is used by default, butCURLPIPE_MULTIPLEXis specified in the sectionDefault.