You’re correct, it did get backported to 6.7.12. So if it’s not working there must be another (perhaps non-obvious) dependency.
commit 4d669d5b7da6311f0a1f124269c4eec141ea7770
Author: Mario Limonciello <mario.limonciello@amd.com>
Date: Tue Mar 5 14:34:24 2024 -0600
drm/amd/display: Use freesync when `DRM_EDID_FEATURE_CONTINUOUS_FREQ` found
commit 2f14c0c8cae8e9e3b603a3f91909baba66540027 upstream.