An unexpected error occurred.

This typically means WordPress trying to connect to the update server in the background, but couldn’t.

This could be due to a simple internet connection issue, or may be the server is temporarily offline, etc. This sort of connectivity issue usually resolves itself after a while.

If not, try contacting your internet/hosting provider.

Also, review this tutorial: https://www.wpbeginner.com/wp-tutorials/how-to-fix-secure-connection-error-in-wordpress/