Shortcuts are on by default. There is no setting to enable, unlike Gmail on the web. Single-key actions fire while a message is selected.
Email triage. r replies all, Shift+R replies, f forwards, e marks as done, s snoozes, d pins, g sets aside, and i marks as priority.
Export to apps uses Option. With an integration connected, Option and a letter sends the current message to that app, for example Option+S to Todoist, Option+O to Notion, and Option+L to Slack. The full list is in the table above.
Compose and send. Cmd+Enter sends, Cmd+Shift+Enter sends and marks as done, and Cmd with a number jumps to the From, Subject, To, Cc, Bcc, or body field.
Formatting uses Cmd. Cmd+B, Cmd+I, and Cmd+U handle bold, italic, and underline, with Cmd+Shift combinations for lists, quotes, headings, and indentation.
A few actions use Control. Mark All as Read is Cmd+Control+U, and opening a thread or composer in a new window uses Control+Option+N.