I think I found the culprit, there are settings in the registry that are probably causing this,
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\cloud\office\16.0\Common\officeupdate]
"updatepath"="http://officecdn.microsoft.com/pr/55336b82-a18d-4dd6-b5f6-9e5095c314a6"
"updatedeadline"="3"
"ignoregpo"=dword:00000001
"enableautomaticupdates"=dword:00000001
"officemgmtcom"=dword:00000000
These settings seem to be retrieved from Microsoft 365 cloud service, as we have not configured them through GPO or ODT. I do not know how to remove them though. Apparently there is a Service Profile in play here, without any Service Profile being deployed.