Which operating system does the issue occur on?
MacOs
If on linux, are you using X11 or Wayland?
Nah

If i run tmux which has an emoji (from https://github.com/Goles/Battery, run which battery -pt, result is #[fg=green][100%] ⚡#[default]%) in status bar, iTerm2 display it probably but alacritty seem broken.

Left side is iterm2, right side is alacritty