If the user's computer has a low resolution, the recorded video will be limited to the highest resolution supported by the user's computer.
For instance, if the display resolution of your computer is 1920*1080 and you choose a higher resolution ratio for recording, the video will still be recorded in 1080p because of your computer's resolution limitations. Similarly, if the display resolution of your computer is 720p and you select a higher resolution ratio for recording, the video will still be recorded in 720p due to the limitations of your computer's resolution.
It is recommnded to select the highest resolution available for recording.
Related instructions:
How can I achieve a 4k resolution recording/video on Mac
Why is the video I recorded blurry