... starting with JupyterLab version 3.4.
When configuring your JupyterLab (version 3.4 and up), you will now find a "Kernels and Extensions" tab. Default extensions and kernels are preselected, so if you do not want to change your Jupyterlab experience, you can ignore this tab entirely.
Only selected options will be loaded at the start of your JupyterLab. If you deselect all options, you can have a more minimal JupyterLab (see example below). JupyterJSC's JupyterLab comes bundled with a few extensions that you won't be able to (de)select (for example many of those in the left sidebar), so you won't be able to start a true "freshly installed", no bells and whistles JuptyerLab this way.
Default kernels selected
No extra kernels selected