The Fitbit Charge 6 used to upload to strava with elevation on hikes bikes walks even though it does not have a built in altimeter, so it has never been possible to track elevation directly with the Charge 6. The GPS chip in the Charge 6 is not designed to display elevation, as it can be very inaccurate.
The data i used to see was actually calculated by Strava, and not Fitbit (i.e those who weren’t connected to Strava - or similar app - never saw that data). It seems that there is a recent issue (since Jan 7th 2026) where Strava is no longer able to calculate correctly or just shows 0 (which is what stand alone fitbit is designed to show).
One suggested work around :
Use "Adjust Elevation" on Strava: Open the affected activity on the Strava website (desktop), click the three-dot menu, and select "Correct Elevation". This forces Strava to recalculate the elevation based on your GPS coordinates and their mapping database.
But basically I think you need to go through Strava for a fix.
So strava can you fix it please?