Not a diaper bag but a diaper backpack? You won't find any problems with us Fairly produced, minimalist, cool and unisex backpacks that suit your needs.
PS: You are going to be parents! 🥳 No reason to change your style.
You can continue to use all backpacks as a work backpack, sports bag, family backpack, etc., even after the diaper change period. The body made of Cordura or recycled PES is guaranteed to withstand a lot.