Inside a room you can set the video quality to 1080p, 720p or 360p. This will affect both when sharing your screen to others, or just recording your own screen.
Video quality will affect both the performance and file size. Therefore it's not as simple as saying "the higher, the better". Some actually prefer a lower quality due to these factors. Also, if you're testing a UI you've created, chances are that you know how it looks and don't need that super high quality to understand where users are looking.
Eventually, what you're gonna test and where you're located is what will rule your decision. It could be that you're on a guest network, or want to save bandwidth. In that case, lower quality is more suitable. But if you're testing something with much text, a higher resolution would be a better pick.,
Our recommendation is to test the video quality before conducting an actual user test.