is it possible for 1 person to operate a motor yacht without any crew members assisting?

True

Motor Luxury yachts if you check the accommodation and I am talking about sail boats to use your quaint American Phrase!

Will have cabins for surprise surprise Crew!

That also goes for motor yachts and before we have our usual collection of pretend captains springing to the Quarter deck to try and put that down is an expect-able expression.

Crews quarters are not there because they are not needed!

Yes of cause you need a crew!

Trying to operate motor Yachts and sailing Yachts of the size and type in the class of being described as luxurious single handed is both insane and suicidal.

Some of the smaller ones could be reasonably handled by a small family.

That is to say the average yacht which is vastly over hyped as luxury Craft.

And I am will to bet most of the stories you have heard are just that stories!

International regulations require all yachts over a certain size to have a crew.

There are exceptions to this such as the Vendee round the world single handed race etc.

really depends on your experience and the size of boat-and type.

most boats of any size are ok for one to handle when out at sea, it's docking and setting sail where more than two hands are often needed.

my own thoughts are that, under most conditions, one person can handle a boat up to say 36 foot. with, a lot of forward planning , with plans B and C on hand if A goes pear-shaped.

without experience, forget it unless you have a very good insurance policy, because chances are there WILL be damage.

frequently done in yachts under 50' however much easier, safer & more fun with a crew.