It doesn’t. I’m running FRITZ!OS 7.25.
I contacted AVM support because I noticed that at least my box would not return to a fixed channel I set manually. You can set a fixed channel manually, which avoids the problem, but the box will still switch to a different channel when it discovers interference, so far so understandable. However, the box should switch back to the channel which was set manually once the interference is gone according to AVM documentation, and my box never does that (at least it seems like that to me).
Support was helpful in listing options I could change, basically amounting to avoid 5GHz for troubled devices, which I don’t want to do because 5GHz works totally fine on channels below 116.
And they said if the box didn’t return to the fixed channel, this would mean the interference wouldn’t be gone. But I can set the channel just fine manually again when I discover connection trouble, and then the channel works fine for a while again.
Since the internet tells me the Fairphone 3 is not the only device troubled by channels 116 and upwards, and since the internet tells me there even are devices supporting only a few channels at the bottom of the range up to channel 48 or something, I proposed that AVM could implement a setting so that the user could set a range of channels which the box would limit its attempts to change the channel to due to detected interference.
Support said they forwarded this for consideration. With this, at least the issue at home would be avoidable reliably. As for being somewhere else, I accept WiFi as flaky tech along with USB and Bluetooth … it works, unless it doesn’t for (too) often mysterious reasons, not much use to expect or bother too much 
.