Question about Fairphone Fairbuds XL 2023

Never tried it yet. But in places where there are a lot of people with headphones or other Bluetooth devices (bus, railway station), I haven't had any problems so far.
Maybe that will help...

This depends very much on the room geometry, the distribution, other devices and sources of interference. WLAN, for example, operates in the same frequency range. I use them every day in an open-plan office and generally have no problems. I only sometimes have to switch from aptX HD to aptX, but I can't say for sure whether this is a problem with the Bluetooth antenna on my laptop. I have never noticed a reduction in audio quality. However, these problems generally occur with all Bluetooth devices, especially headphones, which require a constant connection.