悶 is a traditional Chinese hanzi, listed here under the keyword “gloomy”. It is built from 門 (gate) and 心 (heart). It appears as a component in 2 other characters in this index.
On KumiJi Glyph Explorer, open the parts search and type “gate” + “heart”. 悶 is among the results, together with every other character containing the same shapes.
Open 悶 in the interactive kanji search
to expand every part down to its smallest pieces, add your own names and mnemonic stories,
or search for other characters by their parts.