In RVSM airspace the autopilot (specifically, the altitude control system)
should be used during cruise, in Europe and elsewhere.
RVSM
In-flight procedures.
An automatic altitude-control system should be operative and engaged during level cruise, except when circumstances such as the need to re-trim the aircraft or turbulence require disengagement. In any event, adherence to cruise altitude should be done by reference to one of the two primary altimeters. Following loss of the automatic height-keeping function, any consequential restrictions will need to be observed.
You will find the same language in FAA (AC 91-85B), EASA AMC, etc. So if you choose to hand-fly and... "something happens"... then you're on your own.