Open Messages for me
Action
Shortcut
Open Messages settings
Command-Comma (,)
Hide Messages
Command-H
Hide everything except Messages
Option-Command-H
Quit Messages
Command-Q
Go to a pinned conversation
Command-[number] (press 1 through 9 for the pinned conversation you want)
Go to the first unpinned conversation
Option-Command-1
Open the Emoji & Symbols window
Control-Command-Space
Minimize a window
Command-M
Enter full-screen view
Control-Command-F
Make the text bigger
Command-Plus Sign (+)
Make the text smaller
Command-Minus Sign (–)
Insert a line break or create a new paragraph in a message
Option-Return or Shift-Return
Delete a single message
Delete (first, Apple Support article: Mac keyboard shortcuts