めちゃくちゃ忘れるVSCodeのショートカット二大巨頭。

expand selection

Keyboard Shortcut: ⌃⇧⌘← or ⌃⇧⌘→

Visual Studio Code Tips and Tricks

duplicate selection

Shift+Option+Down and Shift+OptionUp

editor - How do I duplicate a line or selection within Visual Studio Code? - Stack Overflow