This is a known bug in st when the default emoji font contains color emojis. Explained here: https://github.com/LukeSmithxyz/voidrice/issues/284

One of the simplest workarounds is to ensure that the default emoji font is black&white; the linked issue above suggests other workarounds.

Also in the official st FAQ: https://git.suckless.org/st/file/FAQ.html

(search for "when trying to render emoji")