Can I just leave my door open if my room smells like smoke?

Opening the door does help with air circulation, but this measure alone is simply not enough. It cannot fundamentally solve the problem of the smell of smoke.
The reason is simple: The smell of smoke is not just a gas floating in the air; it contains a large number of tiny solid particles (such as tar, nicotine residues, etc.). These particles will quickly settle and adhere to all surfaces in the room, including the walls, carpets, furniture, bed sheets, curtains, etc. Even if you open the door to allow air circulation, only a portion of the odor molecules suspended in the air can be removed, while the smoke dust adhering to the surfaces will continuously release unpleasant odors into the air.
The potential problems that may arise from merely opening the door:
Smoke diffusion: If the room is adjacent to a corridor, living room or other rooms, opening the door will actually cause the smoke to spread to a larger area within the house, thereby expanding the range of unpleasant odors.
Tackling the symptoms but not the root cause: When the door is closed, the smell might be quite strong. After opening it to ventilate, the smell improves somewhat. However, once the door is closed again or after a period of rest, the smoke particles adhering to the surface will release a noticeable smoke smell once more.
More effective approaches (in the recommended order):
Open the window + Fan: By opening the window to create convection and using an electric fan to blow towards the outside, it is much more effective than simply opening the door alone.
Deep cleaning: Follow the previously mentioned procedure to wipe all hard surfaces, clean fabric items, and treat carpets and sofas with baking soda.
Using an air purifier: Choose a model with an activated carbon filter, which can absorb the smoke particles.
White vinegar/Activated carbon: Place several bowls of white vinegar or activated carbon packs in the room to help neutralize/absorb odors.
Conclusion:

Opening the door alone is not recommended. Because it cannot completely eliminate the odor and may even contaminate other rooms. The best approach is to open the windows for ventilation, combined with cleaning and absorption methods, to truly solve the problem. If opening the windows is not feasible due to certain conditions (for example, the room has no windows), then opening the door and installing an exhaust fan (pointing outward) is a less ideal option, but still requires subsequent deep cleaning.