Applies toONTAP 9.x
According to the document Snapmirror Limitation, it has mentioned "You can fan out a maximum of eight destination volumes from a single source volume".
However, it has no hard limited in ONTAP to create 8 fan-out Snapmirror relationships. You are able to create more than 8 fan-out Snapmirror relationships from a single source volume.
The limitation is for performance concerns.
To creating more than 8 fan-out Snapmirror relationships from a single source volume is an un-supported configuration.