Hi @Chexpeare, welcome to the SonarSource Community!
Our instructions reference relative paths; it’s up to you to ensure your absolute paths are valid references to what actually resulted from unzipping the software. You did unzip it, right? If not, please do. If you did, it probably resulted in something more like /opt/sonarqube-9.0-12345 and not the plain /opt/sonarqube you seem to be expecting unless you were careful to rename the resulting directory.
Depending upon your goals, for personal workstation use, SonarLint may be more suitable for seeing static analysis results within your IDE. It will give you all the same bug and code smell detection capabilities as SonarQube. Only security-related concerns will be missing.
Generally speaking, customers run SonarQube in a central location for the benefit of teams and incorporate its analysis into an automated CI pipeline.