Self-service update of credit card details - how to notify staff to re-process recurring contribution?
This works in core! There is an activity created of type Update Recurring Contribution Billing Details when a contact updates their details through the form. And then you can add a CiviRule to send an email when this activity is created. That will also capture back office updates and ideally it wouldn't but this is bearable. A back office update will have a target contact while a self service one will not, but I don't think there is any way to add lack of target contact as a condition in Civirules.
What I did is to only trigger on source contact activities and exclude updates with the source contact ID of one of our staff who might update a credit card from the CiviRule. Not pretty, but good enough.

Not sure if this always worked and somehow my testing didn't work before or something was fixed in our latest update to 5.35.1.