There is not normally any requirement for M-M departure separation for wake turbulence separation.
FAA pilot/controller basic training manual gives no requirement,
FAA Recat and
UK AIC P001/2015 also give no requirement, but they should be required reading. No odoubt someone has quick access to ICAO DOC.4444 for their version. You will see that the minima are different depending on the state, airport, (mode of operation at that airport), airline SOP, individual pilots etc.
Any stated separation is a minimum and can be increased should the pilot feel the necessity (but
do tell the controller
in advance if you feel the need for separation over their minima).