Both apps handle flipped Unicode text without any special setup, but a couple of behaviors are worth knowing before you send one to a group chat.
The lock-screen or banner preview on both apps uses the phone's system font, not the app's in-chat font, and system fonts on modern iOS and Android generally cover the same Unicode ranges the chat itself does — so a flipped message previews correctly in the notification, not just once opened. On older devices this can differ, which is the same font-coverage issue covered in our guide on boxes showing instead of letters.
Flipped text sent to a group behaves like any other message — it's visible to everyone, searchable in the chat's search bar (though it won't match a search for the normal spelling, since the characters are technically different), and can be forwarded or quoted normally. One thing to note: quoting or replying to a flipped message keeps it flipped in the quoted preview, so a long back-and-forth of quoted flipped text can get genuinely hard to follow.
WhatsApp's bold, italic, and strikethrough formatting (using *asterisks*, _underscores_, and ~tildes~) still works around flipped text, since those are just extra characters wrapping your message rather than something that interferes with the Unicode substitution.