Just wanted to say that after playing around for a long time, I got my desired effect to work! Below is the CSS I ended up using if anyone also wants to accompish this.
.design-layout-poster:hover .image-card-wrapper { filter: brightness(1); transition: .3s; cursor: pointer;}
.design-layout-poster:not(:hover) img { filter: brightness(1);}
.design-layout-poster :hover { filter: brightness(.8); transition: .3s; cursor: pointer;}