I'm also very disappointed with this XT5 bug. The XT2/3/4 all work fine (with clear preview when shutter is half pressed).
To promote this camera as a 'purist photographers camera' with such a major flaw with focus peaking just beggars belief!
If Fuji read this, PLEASE FIX THIS BUG (also note that in low light the peak highlights 'flicker').
I have just looked at my X-T2. Yes, the peak highlights are hidden in the T2, when the first pressure is taken, as opposed to the T5. The viewfinder information is partially cleared in both cameras and appears to be the same to me. I don't know of a way to alter the behavior.
This is a known fact about the XF 80mm. You will notice that as soon as you power on the camera, the clinking stops. I believe it has something to do with the OIS. Fuji has confirmed that this is normal behaviors and that there is no danger to the lens.