An editorial answer about the practical requirements of using one backpack as all your luggage.
1 answer
Yes, provided the backpack holds what the trip requires and meets the transport rules you will encounter. The limitation is usually the load you need to carry, not an obligation to bring a suitcase.
Start by separating necessities from conveniences. Documents, required medication, weather-appropriate clothing and essential equipment need a place. Extra footwear and duplicate accessories should earn theirs. A longer journey can work with a small clothing rotation when you have a realistic washing and drying plan; carrying fewer clothes does not remove the need for clean ones.
Do a complete rehearsal rather than testing clothes alone. Include toiletries, chargers and anything used on departure morning. Wear the loaded bag and check whether you can reach a layer or important item without unpacking the wardrobe.
Also decide what happens during day outings. You may be comfortable emptying the main backpack at your accommodation and using it lightly, or you may want a small foldable secondary bag inside it. Neither approach changes the basic one-bag packing discipline. The goal is a load you can manage throughout the itinerary, not winning a contest for the fewest possessions.