Assuming I have to deal with an Automate-newbie, best what I found is:
1) inform the user that to turn off notifications (or notification sound only) he has to choose a (custom) Notification channel for each flow separately
2) if he has such channel, I should let him choose one with Notification channel pick (e.g. for specific dialogs only) or tell him to do it under the flow's description (for whole flow)
3) if not – point him (with App start block) directly to com.llamalab.automate.prefs.NotificationSettingsActivity (and maybe describe what to do there).