This repository contains an outdated SlackBuild and archived. Use the version from official SlackBuilds reposistory instead: https://slackbuilds.org/repository/15.0/academic/qucs-s/?search=qucs-s
git clone https://github.com/ra3xdh/QucsS.SlackBuild
root
:cd QucsS.S.SlackBuild
./qucs-S.SlackBuild
txz
package with installpkg
See https://ra3xdh.github.io/ to learn more