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.
Environment
Debian Testing (Trixie)
Java 17
Can confirm in 24w03b. The server icon, name, ping, and description seem to all be based off the relative size of the screen, whereas the selector is a set size. This may be intentional.