GA support of Juniper QFX5120 for Integrated DCI (VXLAN Stitching) has been introduced in Apstra 5.0 with RFE-3177:
EVPN VXLAN Stitching support for QFX5120 running 23.4R2 or greater is now fully supported (Apstra and platform).
Following incremental configuration is added, which requires a PFE restart: 'set forwarding-options evpn-vxlan vxlan-trans-vni-enable'
As Symmetric IRB isn’t included in older Junos (e.g., 22.4R3/23.2R2) for VXLAN stitching (AOS-43921), you must use Junos 23.4R2 or higher.