What negative effects should I look out for, considering my Canyon Carbon fork without spacer on top, not even a topcap?
The usual problem is that the stem walks up the steerer, so the headset bearing preload disappears and your steering gets sloppy. Crushed steerers are less common, and usually only happen if the highest steerer clamp bolt is very close to the top of the steerer. If one of the clamp bolts is actually level with or above the top of the steerer, stop riding the bike immediately and sort it out.
The usual problem is that the stem walks up the steerer, so the headset bearing preload disappears and your steering gets sloppy. Crushed steerers are less common, and usually only happen if the highest steerer clamp bolt is very close to the top of the steerer. If one of the clamp bolts is actually level with or above the top of the steerer, stop riding the bike immediately and sort it out.