Reproducible on the Multiplayer screen (MC 1.19.1 - 1.20.4, 23w51b), the highlight border of the selected server may get offset by 1 pixel depending on the window width, likely due to some slight rounding issues.

This is not reproducible with Minecraft's default windowed resolution (854x480), but are reproducible on for example (855x480), (1920x1000) etc.

This is most apparent when slowly resizing the window horizontally, the border does not always move with the rest of the GUI screen element.