This documentation is not using the current rendering mechanism and will be deleted by December 31st, 2020. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
Installing with DBAL enabled right from the start isn't as easy as it may seem. You need to have two extensions (the DBAL itself and the ADOdb library) installed before even setting up the core system. How this can be done is explained in this section.