Both use poetry and symbolism to further the storytelling.
Both explore the melancholy and regrets of the MCs. The way both movies are shot gave me the same calm but also shattering atmosphere around the MCs.
Both portray LGBTQ+ relationships.
Moonlit Winter also depicts the MC’s relationship with her family.

The format is different (one is a movie, the other is a drama), but I found SLSYT pretty similar to My Mister in some ways. They both use beautiful symbolism to add to the story.

Both are centered on the MC’s introspection and explore through them regrets that pile up in one’s life and the inner self you never let out all this time. The desire to become somebody else or to disappear out of self-hatred is one of the main themes of both stories.

SLSYT shows the journey of one character, My Mister the meeting of two characters at the lowest point of their life.

The two stories are filled with melancholy and just as Shim Hee Sub in SLSYT, Lee Sun Kyun and Lee Ji Eun/IU portray it in a compelling way.
They both depict the MCs' relationship with their family.