If you right-click on the window capture, there is an excellent option called Resize Output (source size); this will give you the required output without the issues of OBS saying your canvas size isn't value or black lines.
This worked for me to prevent black bars from being recorded. It is the easiest and fastest way for me. This is my experience.
At OBS [Sources] box, right click [Window Capture]>click [Resize Output (source size)]>click [Yes] will prevent all (top, bottom, left, right) black bars from being recorded.
At OBS [Sources] box, right click [Display Capture]>click [Resize Output (source size)]>click [Yes] will prevent top and bottom black bars from being recorded. Left and right black bars still appear in the recorded video.
(note: beside the [Window Capture] or [Display Capture] there is an [eye button] or [eye with slash button], press either button to set it to [eye button] so that source is enabled then the [Resize Output (source size)] will be available)
(note: use VLC media player because by default it will play the exact size of the video so it is easier to see if the video has black bars, the player that comes with Windows 10 (Media Player or Windows Media Player) might play using the last size that the software was closed so you might see the left and right black bars of the software)
