navigator.xr.supportsSession was replaced in the WebXR spec by the navigator.xr.isSessionSupported method in September of 2019 after receiving feedback on the API shape from the TAG. It has been marked as deprecated in Chromium since then, producing a console warning redirecting developers to the updated API. Usage of the call is very low, as shown here: https://chromestatus.com/metrics/feature/timeline/popularity/2416 Additionally, all major frameworks that are used to build WebXR content have been confirmed to have been updated to use the newer call.
API was updated in 2019 after TAG feedback and the older version of the function has been marked deprecated ever since.