I've seen this topic in earlier questions and am having the same problem. The only solution I see is turning off the "Apply Tone Curve and/or "Exposure Bias" in Development Manager. These actions didn't work. I have a Canon 80D and shoot RAW + JPEG. I also read that there may be a problem with Picture Style Settings in the camera, but the answers were vague. My camera is set to Auto for picture style. If I open a RAW file in Canon DPP software or on my desktop with windows the picture appears with normal exposure, but in Affinity it is much darker. I have to increase the exposure on the tools palette between 1.0 and 1.8 to have the picture be close in exposure to the files opened in other applications or the JPEG.
If anyone knows a fix for this, it would be appreciated.