Can B2C Commerce Einstein be Enabled on Sandbox Environments?

Testing B2C Commerce Einstein in sandboxes is not supported. You can test in your site's Primary Instance Group (PIG) instances, i.e. Development, Staging, and Production once the prerequisite steps have been completed for your site. 

Note:

While B2C Commerce Einstein isn't officially supported in sandboxes, it is also not disabled. Feeds are pushed from Production catalogs, and the test instance must match these catalogs, otherwise, issues might arise with tagging, anchors etc. Additionally, since sandboxes run on different resources than PIG instances, it's difficult and often impractical to match catalog sizes. This is why testing is most reliably performed in a PIG instance.