In order to secure an environment, IT Admins choose to work with a security package that includes antivirus software that can be purchased as a standalone option. In the case you are using another antivirus product that is different than Windows Defender, you might need to make sure that Windows Defender is disabled in order to allow your specific antivirus product to run correctly.
This is easily achieved with one of the following methods: using the Registry Editor (by setting the DisableAntispyware property to 1 in HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender) or the Group Policy Editor (via an Active Directory GPO that enables the Turn off Windows Defender Antivirus policy), depending on your version of Windows.
However, when you use the HEIMDAL Agent, a system requirement for our Next-Gen Antivirus with XTP to work is to make sure that Windows Defender is enabled and that nothing is preventing it from running. To make sure that Windows Defender remains enabled on the endpoints in your environment, make sure you are not pushing any Active Directory GPOs that configure it. In the case you have an Active Directory GPO that configures Windows Defender, you need to disable/delete it.
An Active Directory GPO is configured on the Domain Controller, in the Group Policy Management -> Your forest -> Domains -> Your domain -> Group Policy Objects -> Your GPO.
The Windows Defender configuration is done by right-clicking the GPO and hitting Edit. In the Group Policy Management Editor, under Computer Configuration -> Policies -> Administrative Templates: Policy definitions (AMDX files) -> Windows Components -> Windows Defender Antivirus you need to make sure that the Turn off Windows Defender Antivirus policy is Not configured or Disabled.
In case there's another tool configuring Windows Defender, you need to check the DisableAntispyware property in the HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender in the Windows Registry and delete the property or change its value to 0.