RE: U2518D, tearing, stuttering
I watched all of the videos, specifically at the times you mention, twice. I did not see any tearing or stutter. Warranty wise, I see nothing in these videos that would support Dell exchanging this monitor.
Smart HDR is a setting in the U2518D OSD (On Screen Display) =
I will forward this thread to the Displays Team for discussion.
Social Media Support
Run the PC pre-Windows diagnostics
Run the Monitor Reset & BID (Built-in Diagnostics)
Out of Warranty Support