Assuming that your Jamf Settings -> GSX Connection -> "Test" (lower right) also fails, but your GSX cert expiration is still valid?
We got this email the other day from Apple. Not directly connected to GSX, but the timing is suspicious, relative to other things Apple's email (below) says will be affected. Check your Apple Business/School Manager account (Settings -> Enrollment Info -> Terms & Conditions)
"On October 25, 2021, Apple will post updated versions of operating system software license agreements to Apple Business Manager. Once posted, your organization won’t be able to enroll devices or deploy new apps until an administrator has signed in to Apple Business Manager and accepted the following terms:
iOS and iPadOS Software License Agreement
macOS Software License Agreement
tvOS Software License Agreement"