Problem

With the Deprecation notice on JIRA Cloud, Add-on such as "JIRA Auto Watch" is not functional on JIRA Cloud and the Atlassian Development team is not working on the Add-on anymore.This will cause any current usage to stop working as some users prefer to use such configuration to inform certain members on their team.

Workaround

So as an Alternative to those users who would like to continue using such feature, there's an Alternative which can be done with this Free Add-on "Automation Lite for Jira"

After, you have Installed the Add-on on your Instance, you can use this simply Automation Rule to configure a similar attribute that was done by "JIRA Auto Watch".