40L for everyday carry, I’d guess a lot of everyday bags are 30L-35L.
I used a couple of courier bags until I mangled my IVDs. One was a mid-sized timbuk2, the other a larger RELoad. The latter I used for several years and aside from being more flexible was otherwise unharmed by daily commutes and international travel with every day stuff, 2 laptops on trips, and notebooks and so on.
once I mangled my back I needed to use a backpack. A small, tough one. Like the OP I’m not a fan of most ‘laptop backpacks’. I use a cactusoutsoor Portal backpack. 35L, but big enough for everyday stuff, macbookpro in a sleeve and a work Lenovo plus adapters. Aside from the polythene coating peeling off the inside of the outer pocket that Portal continues to be very hard wearing. I’m sure there must be very similar bags available closer to home.
‘tactical’ bags. I kind of like these but they sometimes look a bit OTT with their molle malarkey. And they often seem narrow and deep.