There's a tutorial here Setting up a local web server on macOS 10.13 "High Sierra"
localhost works but user shortname - fails.
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Like on Sierra vhosts seem to need to be activated
sudo vi /etc/apache2/httpd.conf
and uncomment the following lines by removing the hashtag (#)
.#LoadModule vhost_alias_module libexec/apache2/mod_vhost_alias.so
sudo apachectl restart
and you'll be good to go