16:9 screenshots
Here's how I make a Safari window 1280x720 (for some reason you have to set it a bit bigger, probably the Mac shadow or something like that).
osascript -e 'tell application "Safari" to set bounds of front window to {100, 100, 1380, 820}'
That gets me screenshots at exactly 16:9.
For terminal screenshots I use WezTerm with the Tokyo Night theme. It has its own config (still tweaking it, but it'll end up in my nix-darwin config, which I'm leaning toward making public).
That way all the screenshots come out the same, lined up like a ruler, just how I like it.