At the end I still returned the Shine 5 because the small front-facing LED kept shining for no reason. I don’t know if it was hardware related or happened because of the firmware switch.
Which sadly does not work very reliably. At least on my end the selection changes back to default every few days. I reported this issue over the Apple Feedback app already…
Yes, that’s my experience too. I have to choose during each call by opening the control centre and choosing the audio settings option for the ongoing call.
This does seem to let me enable voice isolation though, which seems to work very well.