Action that is executed on bandwidth overuse can be controlled with account form components. If you want to enable it you will need to create a new drop-down form with those items:
- Limit ports speed, with Value passed to App set to "limit"
- Suspend account, with Value passed to App set to "suspend"
- No server action, only notifications, with Value passed to App set to "notify"
Bellow you will find a json form configuration file that can be imported your Proxmox product, this will create an admin only field.