Hi, Roberto.
While not accomplishing what you are looking for 100%, an administrator can set the default option for all forums to be "Forced subscription". This will cause all new forums to have this selected from the beginning, but an user with the appropriate privileges will be able to overwrite it on each. This is done here: https://[MoodlePath]/admin/settings.php?section=modsettingforum
An additional resource: https://docs.moodle.org/311/en/Forum_settings#Subscription_and_tracking
While not accomplishing what you are looking for 100%, an administrator can set the default option for all forums to be "Forced subscription". This will cause all new forums to have this selected from the beginning, but an user with the appropriate privileges will be able to overwrite it on each. This is done here: https://[MoodlePath]/admin/settings.php?section=modsettingforum
An additional resource: https://docs.moodle.org/311/en/Forum_settings#Subscription_and_tracking