I have been using the Ortlieb Backroller with the Commuter Insert for my laptop.
https://www.ortlieb.com/en_us/f3906
That has been working great over the past years. I normally leave the insert in the bag and just unclip the pannier and use the pannier with the shoulder strap when walking between the bike and my desk. And in case I want to use the pannier when not commuting I just pull out the insert and leave it at home.