Slider: Best Practice for Mobile

Hello,
I’d like to share a question that has been on my mind for a long time.

Usually, the websites I create have a section with a content slider, featuring slides where the background image is approximately 1920x1080.

When I audit the websites, they usually score well on desktop, but not so much on mobile (they often fail in the Core Web Vitals).

My question is:
Regarding fast site loading on mobile, which is the better option:

1 - using the same 1920x1080 image for both desktop and mobile in the slider;

or

2 - using a 1920x1080 image for desktop and a smaller, mobile-optimized image for mobile?

In the latter case (2), when viewing the slider on mobile, are both images downloaded or only the smaller one?

Thank you.

Nuno F.