After isntalling the package on M2.3.0 CE, please edit code in file
Bss/MultiStoreViewPricingCatalogRule/Model/Indexer/ProductPriceIndexModifier.php
from
public function modifyPrice(IndexTableStructure $priceTable, array $entityIds = [])
to
public function modifyPrice(IndexTableStructure $priceTable, array $entityIds = []) :void