Hi Manuela,
Until August 2023, J2Store has been updated to Joomla 4. When Joomla 4 came out, there are requests from other customers to migrate JA Mixstore template to J4 so we must update this template to J4 without J2Store. That's why the quickstart package of this extension doesn't include sample data for J2Store.
There are 2 options for now:
1/ Install quickstart package of Joomla 3, it will include data for J2Store
2/ Install Joomla 4 with this template but it will use the default style of J2Store. Joomla 5 has been released, our JA Mixstore will be available to Joomla 5 soon so to be honest, I don't know whether or not this extension could be updated to Joomla 5 and if you use Joomla 4, you will need to wait for the compatibility of J2Store with J5 if you want to migrate to J5.
Regards