It would be useful to have a config option to disable the welcome message introduced in MDL-71964.

This is desirable for SSO environments where the user has already logged in to other non-Moodle services and transferred seamlessly to Moodle from them. In this scenario, the user has already been "welcomed" at an earlier stage outside of Moodle so being welcomed a second time in Moodle looks a bit odd.

The only workaround for this I've come up with short of a custom core patch is to insert the following into an existing custom plugin in my customers Moodle site that listens for \core\event\user_loggedin:

$USER->core_welcome_message = true;
if (empty(get_user_preferences('core_user_welcome', null))) {
    set_user_preference('core_user_welcome', time());
}

Which prevents the welcome message from showing by updating the preferences that controls it before the code that shows the welcome message is executed.