I just looked in my work address book - organisation of 3000+ people and there is not a single Magnus!
Well, that's not surprising, surely. Names go through up and downturns like fashion. I just looked it up, and it's only been in the top 500 in England and Wales since 2014, though more widely used in Scotland.
I know three, but none are over ten. The comedian Ed Byrne has a Magnus, I think.