Someone asked me today if it was possible to use orphaned activities on the front page of their Moodle.
Well the Front Page is a course in Moodle, but an unusual course. You don't have topics, so you can't delete a topic and orphan activities this way.
You could have another course that contains the activities that you link to, but hiding that course may be difficult.
One easy solution though if you have Moodle 3.3 is to use the stealth activities. Activities in any course, including the front page, can have their "Availability" in the "Common Module Settings" set to the new "Make available but not shown on the course page". You can then link to these resources and activities.