Part of vim's keybinding philosophy is to use the easy-to-press keybindings for the common operations. That is why you can use dd instead of using the lesser known whole-line-text-object _ and pressing d_.
For Visual Line Mode, I found that the by far most common task I perform is to expand the selection one line down. The default keychord for that is Vj (or Vjj for three lines and so one). This isn't an inconvenient keychord, but same as d_ there could still be a better one.
In the spirit of assigning the most frequent task to a repeated keypress, I found mapping V to j very pleasant. It enables us to use VV for two lines, VVV for three lines, and so on. While the number of keystrokes stays the same, it reduces mental overhead (the number of Vs to press is the number of lines you want), and saves us the trouble using a second key and also releasing the shift key. It's seems minor at first, but same as with dd or d_, it makes a difference when you do it very frequently.
1vim.keymap.set("x", "V", "j")
Caveat: You cannot use V anymore to exit visual line mode, so you have to use <Esc> for that. Moreover, since vim mappings do not distinguish between Visual Mode and Visual Line Mode, you cannot use V to switch to visual line mode from visual mode. However, I personally find both drawbacks to be negligible.