Custom stride length still doesn't work on Vivosmart 4

2376364 said:

I recently got a Vivosmart 4 for running, and setting a custom running stride length doesn't seem to change the estimated distance when I run.

That's not the designed purpose of the custom stride length. From the article The Step Distance Recorded on My Garmin Watch Is Wrong | Garmin Customer Support:

NOTE: Setting a custom stride length will only impact your calculated step distance. Your custom stride length does not have any effect on the distance recorded for timed activities.

In other words, the only value the custom stride length influences, is the daily Total Distance on the Steps screen.

For adjusting the distance in activities, you have to calibrate them while you use GPS. Calibrating the Treadmill activity (can be done even without treadmill, with a plain walk w/o GPS) would improve the estimate for GPS-less activities too: How Does the Treadmill Calibration Feature Work on My Garmin Watch? | Garmin Customer Support