Denotes that something appears to be (...). It is like そう, but used for emotions.
It is more limited in what words it can be used with.
It itself is a , 形容動詞 (な-adjective) meaning it must have a な.
あの人は寂しげな目をしている He has sad -looking eyes.
高橋くんは不安げに手を上げました Seemingly nervous, Takahashi-kun raised his hand.
眠たげな声でおはようっていった。 With a sleepy voice, he said "good morning"
Sources
https://jlptsensei.com/learn-japanese-grammar/げ-ge-meaning/
https://bunpro.jp/grammar_points/げ