I find it very confusing to get a good workflow with it + calibre.
I sync all of my books (and use readarr for organization or occasionally grabbing books from dead authors) via syncthing. Then calibre web won't ingest any new books I copy to the folder, so I have to go to desktop calibre to add them manually, then it will sync the database and calibre-web has a built-in task for scanning any database changes so then the book will show up.
Seems like a clunky method and I would think I am doing it wrong, but I haven't found a way for calibre to scan books already organized in folders in its book directory.
Ortlieb is expensive as hell but extremely thick, waterproof (resistant?) fabric. I have just a bike bag Urban Roller Plus I think. It is a nice fabric texture instead of smooth dry-packish and it has a nice insert to organize everything and protect my laptop.
My girlfriend has the Various which you can flip the cover over to switch between backpack and bike bag and it is awesome, but more expensive.
Fjallraven is also good, but the strap padding wears out rather quickly. Every teenage girl in Belgium had a Fjallraven pack back when they were in style and every one has the strap pads completely flattened and useless lol.
Dutch company Newlooxs has a couple bike and backpack switchers. The material is thin though and mine ripped open on a fall during my commute.