Linux doesn't serve birth time attribute over NFS

According to this Phoronix article, Linux should support the birth time attribute in the NFS server since 5.18. However, it doesn't show up in the stat output when looking at the file through the NFS mount, or elsewhere (at least, the Dolphin file browser and also a macOS client):

    
% stat file
  File: file
  Size: 0               Blocks: 0          IO Block: 1048576 regular empty file
Device: 0,70    Inode: 103416894   Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/   saiko)   Gid: (  100/   users)
Access: 2023-12-17 03:22:45.368950609 +0100
Modify: 2023-12-17 03:22:45.368950609 +0100
Change: 2023-12-17 03:22:45.368950609 +0100
 Birth: -

  

What gives? Running stat on the server directly, it shows the attribute. The backing file system is ext4, kernel 6.5.12. The client is using kernel 6.1.63.