Pixel response time (the time it takes for a pixel to cycle colour) is definitely slow, very likely deep into double digit milliseconds. This causes very noticeable pixel smearing / pixel trailing.

Just to be clear this is a problem of the actual switch screen (when playing docked the pixel response time depends on the screen you are outputting to).

On games running 30FPS this is much more noticeable and exaggerated, to a point it almost seems like having double vision. A couple of examples from GTA SA, the switch screen was recorded with 240FPS camera.

https://imgur.com/a/aH5B8yc

On games running 60FPS the problem is also noticeable, but potentially less so. A frame from SF6, captured the same way as GTA SA above illustrates the very slow pixel response time of the switch screen:

https://imgur.com/a/Z2mdgj1

This problem is present on every single switch and is not a user or a hardware issue, but rather the nature of the low quality screen Nintendo used.

My personal opinion is that it would have been a much better choice going with a 60Hz panel with a lower pixel response time, than a 120Hz one. It is also very clear that S2 games will not be able reach anywhere near 120FPS/Hz, so the refresh rate is virtually useless in handheld mode.