New Topic notification via email
admin received New topic notification via email. Is it possible that all the members registered received the same mail as well.
Only if they manually subscribe to a specific Forum. Also doing what you ask by default, could create a GDPR issue.
I'm sorry but wpForo doesn't have automatic subscription options.
wpForo has a built-in Subscription Manager tool that makes subscription easy. It can be found in My Profile > Subscriptions page:
Another two options to make topic subscription easy (NOT RECOMMENDED):