Hello,
You could do this by setting up the default indexes that you want to monitor automatically, and making sure that you only add the monitoring to SNMP Device-connected interfaces by default. Here are the steps:
1. Performance Management > Performance Option > Monitor Option > Make sure that the "Interfaces Connected to SNMP Devices" is selected, and the other options are unselected. You can choose whichever option you like for the interface types - usually monitoring physical interfaces only to avoid adding many unimportant virtual interfaces like loopbacks. Click Set to save the setting as default for any interface indexes added to devices.
2. Performance Management > Performance Option > Default Monitoring Indexes > Select all the Interface indexes that you would like to monitor by default. Please be careful selecting indexes here, as they will be added to all interfaces that match the "Monitor Option" settings on all newly added devices in iMC, and adding too many different monitors can overload iMC and its Performance Management. Only add what you really need to monitor.
3. Once all the default indexes you need are selected, you can click Save to add them automatically on all relevant interfaces of devices added to iMC in the future. Clicking Add Indexes will deploy the monitoring to your existing devices instead/as well, while Cancel does the opposite.