You can get all the CMS Static Blocks collection in Magento 2 by calling interface, Magento\Cms\Api\BlockRepositoryInterface.
Magento\Cms\Api\BlockRepositoryInterface used for getting CMS Static Blocks related data in Magento 2.
BlockRepositoryInterface is used when you need to fetch a collection of CMS Static blocks or get specific CMS static block data. You can get Specific Blocks data by Identifier using Get Cms Blocks data by an identifier.