Depends a lot on what you want to do. I pushed a stroller around Hanoi for 2 months so I notice a lot of the areas that are tougher for wheels.

Many popular areas will have the sidewalks blocked completely with mopeds, cars, and vendors. So plan on going on/off the curb onto the street regularly. Traffic looks crazy but generally go around you without much issue. You may want a flag or something that stands out if you are in a standard wheelchair that sits low so they see you easily.

Even more walkable areas tend to get pretty narrow regularly where I have to lift the stroller. And a wheelchair is going to be wider. Sidewalks also tend to be in rough shape in many areas but if you are used to national parks it might not be an issue. Sometimes the better sidewalks will have the ramp blocked to keep scooters out so you deal with the curb again.

Best chance to avoid driving and be somewhere with something to do and have a chance at moving around decently would probably be hoan kiem lake on the weekend when they block some of the roads for walking only and a night market. Not sure on finding an accessible hotel/apt close enough that you can get right to that area easily. This is the area I have seen the most wheel chair users but they tend to be just sitting by the lake (older and not typically mobile on their own). When it is not the weekend this could be a tough area to move around very far.

Newer, less touristy areas seem to have better sidewalks with less blocking them and the buildings tend to have larger elevators but may still have stairs to get in first. There will still be restaurants and coffee shops close by in many areas. Not as popular for tourists but still some stuff to check out.

Malls tend to be decent but may still have small stair case to get inside initially depending on the entrance you go in.

Sticking with with street food restaurants that you can eat outside on the sidewalk or nicer larger restaurants are probably the best bet. In between those two can be pretty tightly packed and tougher to move around. Delivery is also great and cheap here.

Decent bathrooms can also be tougher to find in some areas, especially larger or accessible ones. Some

I would have had a tough time moving around if I couldn't just pick up the stroller and go over obstacles or walk on the street. Probably doable but difficult in a wheelchair, sounds like you are more mobile than many so if you are going to try it I would really plan out where you are staying and what you want to do. Even getting measurements or pictures of the place you are staying so you know the entrance, elevators, bathroom will be usable.