I had an Alienware laptop for the last 20 years that was made of ballistic nylon and was very rugged but is finally showing its age. My laptops are usually around 17". I would put my laptop in the Alienware laptop and it would easily fit.

So as a replacement I got a Swissgear 1900 laptop backpack that seemed to be constructed as ruggedly as the Alienware laptop and claims to be able to hold a 17" laptop. Then I tried putting my laptop in and it barely fits. After zipping it in, the corners are stretching the zipper. The 17" is the screen size, but laptops are more than just the screen.

Does anyone have recommendations for a well made rugged laptop backpack that can hold an 18" laptop if necessary?

I like ogio

I have this one and love it.

https://www.amazon.com/gp/product/B08KXQ3GG9/?th=1

Lots of pockets, place for sunglasses at top, water bottle holder elastic mesh pocket on the side, USB charger port, Headphone port, Lots of pockets

I bought 3 on Amazon and returned the other two.
That is what I recommend. Buy a few and then return the ones you don't want.

I would check out ebags. They're running 50% off right now. I have an older ebags backpack that has a ton of features. They've redesigned them to do more packing for weekend type trips than daily carrying but I think they may have something you'll like. You can search by laptop size.

Seconded, I've been rocking this one for several years and it's great.

https://www.ebags.com/backpacks/laptop/pro-slim-laptop-backpack/117775D636.html

I was going to say to get an old school Dell XPS bag, but the one linked looks way better.

I use this one. Had it a few months and love it so far.

https://www.jonessportsco.com/collections/backpacks/products/a2-backpack-r-clay-green

I got a Timbuk2 laptop backpack for Christmas a couple years ago and really like it. Weirdly get a lot of compliments on it, too....

I use a GoRuck GR2…indestructible, and the dedicated pocket for the laptop is very large, and very protective. But…it is pricey as hell. I travel for my job just about every week, so it was worth it for me.

https://www.goruck.com/products/gr2-heritage-usa?variant=42120699871332