Sorry to say, but that all don't make sense.
flattening it into a relational structure ... be displayed in Tableau report.
Tableau can utilize OLAP data sources, see https://help.tableau.com/current/pro/desktop/en-us/cubes.htm
I am Looking for another solution for how to store OLAP data relationally.
And from where do the source data for the cube comes from; a relational database?
So relational => OLAP => relational => Tableau?