duplicate key error efcore

I'm trying to use efcore but I'm getting a

duplicate key value violates unique constraint "PK_Tags"

duplicate key value violates unique constraint "PK_Tags"

error.
My model contains:

        [Required]
        public List<string> Tags { get; set; } = [];

        [Required]
        public List<string> Tags { get; set; } = [];

however, this is not a key?
I'm updating the value by getting it from the database, modifying it, then calling Update with the modified value.