After latest update, emojis on my iPhone have been messed up

When you say "large emojis" to you me your memoji stickers? If yes, tap the + on the left of the dialog box and then tap Stickers.

Change is a fact of life. Not letting it upset you, might help.

Your emojis are still there, where they've pretty much always been on the left hand bottom corner of the screen. If you want Memoji's or stickers or other options, tap the + button on the left side of the enter text area.

You CANNOT go back to the previous iOS version. Downgrading is NOT supported.

I'd suggest you reach out to Apple for help. We're just users like you on this user to user only forum. The emoji's are all on my iPhone under iOS 17.

If you're in the US, call Apple at 800-MY-APPLE

lobsterghost1 is correct. And to address your other statement, there is no way to downgrade iOS. Apple does not provide a path to do that.