I have been noticing this Receive Alerts button when I am editing a custom object's standard page layout. But when I view a sample record page, it is not displaying.
I am just wondering its real usage since I cannot see any documentations about it. Also, why is it that I can see it in page layout editor but not in actual record detail page?
Not sure if this is correct, but I was also wondering recently the same thing about that standard button. In Spring '21 sandbox preview orgs, it's been renamed 'Get Alerts'.
The API Name is 'IsotopeSubscriptions'. Isotope seems to be related to Salesforce Engage and Quip in some documentation, but also a part of Salesforce Anywhere with these being added user permissions in Summer '20.
My assumption is that it's related to this subscription feature within Salesforce Anywhere. To my knowledge, my org is not part of the beta though, so it is odd that button is visible in the Layout editor for classic and lightning actions.