Cleanmgr has been a great Windows tool for years. Currently it can cleanup up trickier file sets like patch caches and Windows in-place upgrade .old directories.
Cleanmgr.exe /VERYLOWDISK is the command switch that will run a full cleanup (temp files, patch cache, etc.) with the wizard hidden but will show a final window stating the current disk free space. I don’t believe there is a full silent option with the native clean up tool.
The Automox agent should be running the tool as SYSTEM , so I would assume it would run successfully. With it running as SYSTEM however, I’m curious if maybe it does complete the cleanup but any window would be hidden from the current user since the process would be running as the SYSTEM account. This could cause it to report oddly if the process never stops running. Hard to say without digging in.
A note with Windows 10: Microsoft will be deprecating this tool in the future. Not necessarily removing it from the OS, but discontinuing new support for it. Hopefully it will remain like Paint did when they deprecated that, but for now it is a very helpful tool.