Keystore Explorer (https://keystore-explorer.org/) is a trusted open source GUI replacement for the Java command-line utilities. The best feature is its automated import of the signed Certificates, and the ability to view/verify all aspects of the Keystore file. It is not a requirement, but it does significantly reduce the time and problems involved in doing it manually.
It does not create the initial certificate, about the only thing it does not do. It allows full display, creation, changes, and analysis of a Java KeyStore file (.jks). It imports the certificate information and formats it correctly, a process that can be difficult manually because there are 3 files to be imported and they must be in a particular order. The KeyStore explorer puts them in the proper order automatically.