Yes, #nostrudel is browser based. But it does work in https://play.google.com/store/apps/details?id=com.nostr.universe on mobile too.

For bookmarks in #amethyst just tap the little three dots on the top right of a note. In the menu you're able to add the note to a private or public bookmarks list. To see your bookmarks just swipe from the left to right of the screen or tap your profile icon.

nostrudel will show you the public bookmarks from amethyst only.