I just put my laptop in my backpack. I think a lot of people do. In a crash there’s no way to predict how the bike would bounce and hit so I’m not sure if the laptop would be any safer on the bike instead of on you. Some people even feel in a crash the lap top worn in the backpack might help protect your back, but again that’s hard to predict in an uncontrolled event like a crash.
I will say this – I wear a backpack because I have no luggage case on my bikes. If I had luggage cases on my bikes, then I’d be happy not to have the weight of the backpack on me. Still, not a big deal, unless the backpack is really full then it feels kind of bulky on the back.