If you have 'Quick Selection' active (the magnet - the space bar key is the temporary on/off toggle), you should find that you can hover anywhere over the opening in the wall and you should be able to select the door window.
Otherwise you have to select it by the corners of the opening or there should be a centre spot.
Or as mentioned there is usually one at the end of the door leaf.
Also as mentioned, having the door or window tool active and holding SHIFT while selecting, will give priority to selecting the door or window (or element belonging to the tool you have active).
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11