macOS 11 Big Sur and ScheduleOSUpdate

Has anyone been able to test OS Update on macOS 11 (Intel) ?

Status returned by MDM returns the very un-informative message "InstallFailed":

Code Block 
	<key>UpdateResults</key>
	<array>
		<dict>
			<key>InstallAction</key>
			<string>Error</string>
			<key>ProductKey</key>
			<string>MSU_UPDATE_20A5374i_patch_11.0</string>
			<key>Status</key>
			<string>InstallFailed</string>
		</dict>
	</array>

And installer log on the device shows:

Code Block 
020-09-23 11:39:38+02 macmini SoftwareUpdateNotificationManager[828]: (null)：softwareupdated: Service connection invalidated!
2020-09-23 11:39:38+02 macmini softwareupdated[1145]: Removing client SUUpdateServiceClient pid=828, uid=501, installAuth=NO rights=(), transactions=0 (/System/Library/PrivateFrameworks/SoftwareUpdate.framework/Versions/A/Resources/SoftwareUpdateNotificationManager.app/Contents/MacOS/SoftwareUpdateNotificationManager)
2020-09-23 11:39:38+02 macmini softwareupdated[1145]: Removing client SUUpdateServiceClient pid=828, uid=501, installAuth=NO rights=(), transactions=0 (/System/Library/PrivateFrameworks/SoftwareUpdate.framework/Versions/A/Resources/SoftwareUpdateNotificationManager.app/Contents/MacOS/SoftwareUpdateNotificationManager)
2020-09-23 11:39:38+02 macmini softwareupdated[1145]: Fetched MajorOSInfo for productKey:001-36801; getIcon:NO; the SUMajorProduct was fetched remotely.
2020-09-23 11:39:39+02 macmini softwareupdated[1145]: Fetched MajorOSInfo for productKey:001-43966; getIcon:NO; the SUMajorProduct was fetched remotely.
2020-09-23 11:39:39+02 macmini softwareupdated[1145]: Fetched MajorOSInfo for productKey:041-91758; getIcon:NO; the SUMajorProduct was fetched remotely.
2020-09-23 11:39:39+02 macmini softwareupdated[1145]: Fetched MajorOSInfo for productKey:061-26589; getIcon:NO; the SUMajorProduct was fetched remotely.
2020-09-23 11:39:40+02 macmini softwareupdated[1145]: Fetched MajorOSInfo for productKey:061-94403; getIcon:NO; the SUMajorProduct was fetched remotely.
2020-09-23 11:39:40+02 macmini softwareupdated[1145]: SoftwareUpdate: request for status for unknown product MSU_UPDATE_20A5374i_patch_11.0
2020-09-23 11:39:40+02 macmini softwareupdated[1145]: SUOSUServiceDaemon: No agents found to execute MDM major OS command!
2020-09-23 11:39:40+02 macmini softwareupdated[1145]: SUOSUServiceDaemon: No active client to get update status
2020-09-23 11:39:43+02 macmini softwareupdated[1145]: SUOSUServiceDaemon: No agents found to execute MDM major OS command!
2020-09-23 11:40:02+02 macmini softwareupdated[1145]: SUOSUServiceDaemon: Connection invalidated!
2020-09-23 11:40:02+02 macmini softwareupdated[1145]: Removing client SUUpdateServiceClient pid=1124, uid=0, installAuth=NO rights=(), transactions=0 (/usr/libexec/mdmclient)

after reboot, install log shows:

Code Block 
% tail -f /private/var/log/install.log
2020-09-23 11:53:16+02 macmini softwareupdated[533]: MSU updates found: (
	    "<SUOSUProduct: MSU_UPDATE_20A5374i_patch_11.0>"
	)
2020-09-23 11:53:16+02 macmini SoftwareUpdateNotificationManager[727]: Controller: Received availableUpdatesChanged notification; new updates: [MSU_UPDATE_20A5374i_patch_11.0]; new major updates: [001-43966, 001-36801, 061-94403, 061-26589, 041-91758]
2020-09-23 11:53:16+02 macmini softwareupdated[533]: SoftwareUpdate: request for status for unknown product MSU_UPDATE_20A5374i_patch_11.0
2020-09-23 11:53:16+02 macmini SoftwareUpdateNotificationManager[727]: SUOSUShimController: Armed: 0, with mode: 0, date: (null), updates queued for later: (
	)
2020-09-23 11:53:16+02 macmini softwareupdated[533]: Descriptor has changed since previous download (11.0 vs (null))
2020-09-23 11:53:16+02 macmini SoftwareUpdateNotificationManager[727]: SUOSUShimController: MSU update is not yet downloaded & prepared
2020-09-23 11:53:16+02 macmini softwareupdated[533]: SoftwareUpdate: request for status for unknown product MSU_UPDATE_20A5374i_patch_11.0

I tried a few things (with or without SoftwareUpdate profile to enable beta, with or without caching server), but without success.

Is there a way to upgrade Beta macOS via MDM ? Or is this limited to Released versions - but then, why would the device report Beta updates via MDM ?