Some mouses have 2 buttons at the thumb position, they work out of the box in browsers and other apps so the user can move back and forth previous and next page; those buttons don't work on itch app.
As for the mass downloads, it's a really needed feature. I've bought some mega bundles of game assets. I'm happy I can use the app to filter by assets and also I can sort by newest order, but it's a really long scroll, let alone manually pressing every single download button.