Apple has officially blocked the signatures of iOS 13.5.1, a few days since the release of iOS 13.6.

With the block of signatures, the users who have updated your iPhone or iPad to iOS 13.6 can no longer downgrade and return to iOS 13.5.1.

This outage has an impact especially on those who perform the jailbreak, since a potential release of iOS 13.5.1 it would be now useless to those who have already updated to iOS 13.6.