I have a nearly new i7 9th gen Laptop with RTX2060 Gsynch and 240Hz display.
I noticed that I had frame jumps every few seconds when the Display Method was set to Auto. I have frame rate set to 50p, and just read this, which explains that it was using smooth with the versions later than vMix 20. I have found the frames don't jump when I select either Low Latency or Legacy. This was with help from Martin.
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The following is from vmix help
Display Method

This option selects the method by which vMix presents video to the computer display (both for Preview/Output windows and the Fullscreen outputs).
Note that these options do not impact the recording / stream / external outputs in any way, and only apply to the outputs on the graphics card.

Auto Let vMix select the best option based on the current settings. This will usually be the same as selecting Low Latency for frame rates less than 30 and Smooth otherwise.

Low Latency Displays video as fast as possible to the computer display to ensure the lowest possibly latency. Video playback may be less than smooth as a result.
Smooth vMix will make every effort to ensure the video playback is as smooth as possible on the display but may add a couple of frames of delay as a result.

Legacy Use the display method employed by vMix 20 and earlier.
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Has anyone else noticed this difference ? as it would seem to me, that feedback to keep Legacy in, is quite important. Maybe the word could be changed to Normal. I just have a concern with the fact it is called Legacy, might mean that it is removed one day, but I quite like the fact that Legacy appears smoother, and doesn't have the extra CPU or GPU requirement that Low Latency has.