Inside a room, on the top right, you can set the video quality to 1080p, 720p or 360p. This will affect both, sharing your screen with others, as well as just recording your own screen.
Video quality will affect both the performance and file size. Therefore, it is not as simple as saying "the higher, the better". Some users may actually prefer a lower quality due to these factors. Also, if you are testing a UI you have 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 are going to test and where you are located is what will rule your decision. It could be that you are on a guest network, or want to save bandwidth. In that case, lower quality is more suitable. But if you are testing something with much text, a higher resolution would be a better choice.
Our recommendation is to test the video quality before conducting an actual user test.