Never used qtrees as DS but it is a interesting question, and found this official wording from NetApp.
Datastore layout:(Flexvols recommended by NetApp)
NetApp recommends the use of FlexVol volumes and, starting with ONTAP 9.8 FlexGroup volumes, NFS datastores.
Qtree: (Qtrees NOT generally recommended)
Other ONTAP storage containers such as qtrees are not generally recommended because these are not currently supported by ONTAP tools for VMware vSphere. Deploying datastores as multiple qtrees in a single volume might be useful for highly automated environments that can benefit from datastore-level quotas or VM file clones.
VMware vSphere with ONTAP Best Practices - January 27, 2023
https://docs.netapp.com/us-en/netapp-solutions/pdfs/sidebar/VMware_vSphere_with_ONTAP_Best_Practices.pdf