The corners of the image appear slightly distorted when looking through the viewfinder.
Your camera is equipped with a high-resolution, high-contrast organic EL viewfinder, the XGA OLED Tru-Finder. To achieve high viewability, the viewfinder is designed with an emphasis on balancing the various elements.
As a result, while there may be slight distortion at the edges of the viewfinder, it has a 33.3-degree viewing angle and a 27 mm high eye point, as well as 100% viewfinder coverage, providing excellent viewability.
You can use the LCD screen if you want to check the details of your picture composition.