On the OVA deploy wizard there is no option to select for small or tiny witness size.
VMware vSAN ESA 8.x/9.x
The small and tiny sizes for the vSAN witness appliance is not available for vSAN ESA deployments.
Consider deploying a vSAN OSA cluster instead of an ESA cluster. If that is not an option, then for ESA the only options available are medium, large and extra large for deployment size.