The reason is you haven't installed Core module. Please follow this link to finish the installation process: https://www.mageplaza.com/install-magento-2-extension/
You can read more about this error here: https://mageplaza.freshdesk.com/support/solutions/articles/6000107679-500-error-cannot-access-backend-frontend-
Was this article helpful?
That’s Great!
Thank you for your feedback
Sorry! We couldn't be helpful
Thank you for your feedback
Feedback sent
We appreciate your effort and will try to fix the article