Set the value of the HideDefaultThemes setting

• command: spo hidedefaultthemes set -h|--hideDefaultThemes <hideDefaultThemes>
• hideDefaultThemes: set to true to hide default themes and to false to show them

More details: see https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/site-theming/sharepoint-site-theming-powershell#set-spohidedefaultthemes

REST API exposed via https://tenant/thememanager/SetHideDefaultThemes