posthumous work
Refers to a creative work (art, literature, music, etc.) left behind by someone who has died, especially one published or exhibited after their death.
This novel is his posthumous work.
The painter's posthumous works are on display at the exhibition.
This novel became his posthumous work.
The family released the painter's posthumous work.
An exhibition of her posthumous works will be held next month.
遺品 means any belongings or personal effects left behind by someone who has died, whereas 遺作 refers specifically to a creative work they left unfinished or unpublished at death.
Compound of 遺 (い, 'leave behind') and 作 (さく, 'work'). The kanji combination directly conveys the meaning of a work left behind after death.