Make sure you upgrade to SonarQube v9.9 LTS soon, not only to benefit from our Best LTS Ever™, but because soon we will systematically ask users to upgrade when they ask questions about earlier versions of SonarQube, which are now considered unsupported.
There is no reporting in Community Edition, just the Web API (docs link in the page footer) from which you can craft your own reports.
I think you’ll just have to add the LoC of each project. The Projects page will give you an approximate LoC for each project. If you need exact figures and/or you have a lot of projects, it may be easiest to script querying the API.
In addition to @ganncamp’s suggestion, if you don’t need details per project, you may want to look at the System page in the Administration panel. You should find there the total number of lines of code analyzed on your instance.