If you have any YouTube restrictions/setups in the old UI of the Securly Safety Console and shift over to the Nucleus UI, your settings will automatically move to the G Suite YouTube Restricted Mode settings. You can then go ahead and set up YouTube restrictions in the Nucleus UI. These settings will take precedence over any G Suite settings you may have previously configured if users do NOT log into YouTube.
(Note that currently, this feature is only available for Chrome Extension users. DNS and SmartPac users will get this update over the next few months.)