Optocoupler is intended for galvanic isolation of circuits. Isolation breakdown voltage is in range of kV. Secondary element of optocoupler can be phototransistor, thyristor etc. Optocouplers are not primarilly intended for HV switching.
optocoupler is used to feed back from two parts of the design which with two different references.
(mainly for isolation between the two parts)
and it is not designed to control the switching process.
you may use the output of the optocoupler to drive a power transistor or MOSFET to switch the high voltage but the optocoupler are not intended for power switcihng, only for low level signals.