Selecting that option requires scanning all installed plug-ins to detect the ones which report 64-bit processing capability. You could use the resulting list to create a dedicated plug-in collection only containing 64-bit processing plug-ins.
Please keep in mind:
Double precision processing is not available for VST2 plug-ins!
Whether a VST3 plug-in or instrument supports 64-bit processing precision is up to the manufacturer of the plug-ins. Some manufacturers advertise an internal (!) 64-bit processing for their plug-ins but still do not support a complete audio processing in 64-bit double precision throughout the whole signal path.
