Gallery thumbnails appear blurry

Hello,

I’ve noticed that gallery and album thumbnails appear blurry, despite the source image itself being of sufficient size and resolution.

In one gallery, I set the width and height to 0 and 0, so that it would just take the full size of the image which is here: https://dhahanprize.com/wp-content/uploads/dhahan-prize-ceremonies-2022-audience-camera.jpg

See screenshot of setting: https://cloudup.com/c0pUFo9EBvP

However, it still appears blurry.

On a different site, I entered a size of 300×200 like so: https://cloudup.com/ct5dOHHAK8o

It still appears blurry: https://cloudup.com/c0IUXphnX4K

What settings are required to make the thumbnails tack sharp, as their image sources are?