Unfortunately, it is not possible to use the data imported from Google Analytics with any other site in Matomo using the Roll Up feature.

When you import data from Google Analytics into Matomo, only pre-processed reports are imported, and the raw data is not included. Since the Roll Up feature queries the raw data to generate reports, it cannot be used to compare or include imported data from Google Analytics with other sites in Matomo.

Previous FAQ: Will the reports be shown in the Matomo Mobile app for Android and iOS?