On my Mac, with the Cmd + Return configuration to send messages, the Cmd + Return shortcut does not work to send the message when it's in preview mode, but it should.

The Ctrl + Return shortcut does work, which is probably due to the work in #22705.

CZO thread: https://chat.zulip.org/#narrow/channel/9-issues/topic/Send.20message.20via.20keyboard.20with.20compose.20box.20in.20preview.20mode/near/1972836