How to let KDE on Debian show emojis?

I am using KDE on Debian (both stable/Bullseye and testing/Bookworm). Emojis are not displayed in the terminal, not in window titles and not in system notifications. One way to reproduce the problem is to open https://www.youtube.com/watch?v=YaYoJziCgto as it will cause plenty of emojis to be displayed in the window title bar. I only see these "missing font rectangles". Another one is to run echo "Heart Face Emoji 🥰"; it will display an empty box too. The problem does not appear on Xfce/Bookworm and KDE on Ubuntu. The problem persists on KDE/Bookworm when using Wayland. Since the problem does appear on KDE/Bookworm but not on Xfce/Bookworm, I think one can conclude that all required packages, e.g. fonts-noto-color-emoji are installed. I have not changed anything in the font settings. How can I enable emoji rendering in KDE?