Wildcards is in the Title of https://help.libreoffice.org/6.1/en-US/text/swriter/guide/search_regexp.html?DbPAR=WRITER#bm_id3150099, but the explanation seems about regular expressions, what I think can confuse users, at the bottom of the page there is link 'List of wildcards' that links to a page with the right title 'List of regular expression'.
In calc there is an option to select wildcards or regular expression or none. Menu/Tools/Options/LibreOffice calc - Calculation.
Difference between wildcards and regex can be founded in the help about those options https://help.libreoffice.org/6.1/en-US/text/shared/optionen/01060500.html?System=WIN&DbPAR=CALC#bm_id3154420
Wildcards in calc was implemented by Eike for compatibility with excel, in fact when an excel file is open wildcards option it's automatically selected.
In writer only regex are available, not wildcards.
Term regex - regular expression should be used instead and wildcards only like they are in calc help about wildcards selection or should be in calc's help about search and replace.
Regular Expression (LO's C++ ICU libs ) provide Wildcard matching--correctly known as metacharacters and operators.
Prior to Eike's work on textsearch in bug 72196 for Excel interoperability, simple Wildcard--"glob" syntax --based text searches did not exist, and it was convenient to refer to LibreOffice's pattern matching as "Wildcards"
It is now important to make a distinction as globbing ("*" "?") metacharacters are present as operators in ICU Regex but with completely different function.
Given that we support both, I would agree assigning the "Regular Expression" term for our legacy means of handling pattern matching is needed. While relegating "wildcards" use to the specialized glob style searches (currently only supported in Calc for interoperability with OOXML spreadsheets).
Olivier Hallot committed a patch related to this issue.
It has been pushed to "master":
tdf#118076 Clarify use of regexp in writer search