With vSphere 7.0U3d and later, there can be a maximum of 20 concurrent jobs—backups and restores—per ESXi host. The limit is set to 18 concurrent backup jobs or 16 concurrent restore jobs per host. It is a shared pool in which neither backup nor restores can reach 20, so that other restore and backup jobs can run at the same time.
With vSphere 7.0U3c, there is a static limit of 10 concurrent backup jobs and 10 concurrent restore jobs per ESXi host.
There can be maximum of 180 concurrent VM operations per vCenter.