What is the pixel density of your screen? 100% or larger? Blurry rendering occurs when Windows upscales the controls created at 100%. The correct way to handle this situation in Lazarus is to go to the project options, check "Use LCL scaling" and select "on" in the "DPI awareness" combobox.
To me, however, your screenshots do not look blurred. I get similar images (100% - no scaling), and I can confirm that the TBitBtn has these gray extra pixels unlike TButton and TSpeedbutton.
I do not think that this has anything to do with BGRABitmap because the LCL is rendered by native routines, without BGRABitmap.