This can be accomplished with a POST to: https://graph.microsoft.com/beta/deviceManagement/configurationPolicies
Easiest way to figure it out is just do a F12 Developer Tool trace during creation with UI. Then take the Request Body and modify as needed.
Here’s my request body that worked in Graph Explorer to create a basic new policy with one user:
{"name":"Test","description":"test","platforms":"windows10","technologies":"mdm","roleScopeTagIds":["0"],"settings":[{"@odata.type":"#microsoft.graph.deviceManagementConfigurationSetting","settingInstance":{"@odata.type":"#microsoft.graph.deviceManagementConfigurationGroupSettingCollectionInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure","groupSettingCollectionValue":[{"children":[{"@odata.type":"#microsoft.graph.deviceManagementConfigurationGroupSettingCollectionInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup","groupSettingCollectionValue":[{"children":[{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_userselectiontype","choiceSettingValue":{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingValue","value":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_userselectiontype_users","children":[{"@odata.type":"#microsoft.graph.deviceManagementConfigurationSimpleSettingCollectionInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_users","simpleSettingCollectionValue":[{"value":"AzureAD\adam@contoso.onmicrosoft.com","@odata.type":"#microsoft.graph.deviceManagementConfigurationStringSettingValue"}]}]}},{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_action","choiceSettingValue":{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingValue","value":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_action_add_update","children":[]}},{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingCollectionInstance","settingDefinitionId":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_desc","choiceSettingCollectionValue":[{"@odata.type":"#microsoft.graph.deviceManagementConfigurationChoiceSettingValue","value":"device_vendor_msft_policy_config_localusersandgroups_configure_groupconfiguration_accessgroup_desc_administrators","children":[]}]}]}],"settingInstanceTemplateReference":{"settingInstanceTemplateId":"76fa254e-cbdb-4718-8bdd-cd41e57caa02"}}]}],"settingInstanceTemplateReference":{"settingInstanceTemplateId":"de06bec1-4852-48a0-9799-cf7b85992d45"}}}],"templateReference":{"templateId":"22968f54-45fa-486c-848e-f8224aa69772_1"}}