You can access your Flyby by clicking View Flybys on your activity details page on the web. Alternatively, you can manually enter your activity ID into the Flyby tool. You have the ability to opt out of this feature entirely if you do not want your activities to be included in Flybys.

Years ago, Strava unilaterally disabled the flyby feature on all profiles. They did this without any kind of notice so most people figured the feature was removed completely. Only those who dug around could find that it was a toggle setting in the privacy settings that had to be manually enabled for each person.

Selected activities are projected onto your activity path along all sections where you traveled the same path. The colored circles show the projected positions of selected activities. Each colored line plots the time gaps between a selected activity and the main activity. The main activity appears as a flat black line.