Apple on Monday released iOS and iPadOS 13.5.1 to the general public for the sole purpose of patching the new exploit in the unc0ver v5.0.0+ jailbreak tool, and as you might come to expect, Apple will soon unsign the jailbreakable iOS 13.5 firmware.
It usually takes the Cupertino-based company a week or two after a new firmware release before it stops signing an older version of iOS or iPadOS, but in recent memory, just one week has been a lot more common. By doing this, Apple can leave its user base with no option of downgrading or upgrading back to iOS or iPadOS 13.5, effectively preventing users from jailbreaking.