I’m on a MacBook Pro 16". Here’s a screenshot I just captured of the Discourse logo.
That’s too large; it should be displayed at 50% by default.
It’s possible to detect this by reading the PNG metadata. For example, here’s ImageMagick’s metadata:
$ identify -verbose logo.png | head
Image:
Filename: logo.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: DirectClass
Geometry: 312x90+0+0
Resolution: 144x144
Print size: 2.16667x0.625
Units: PixelsPerInch
Colorspace: sRGB
HiDPI images have a resolution of 144x144.
Discourse should detect this situation, and show the image resized down to 50% by default.