It CAN be time based, but there's also a "hot" and an "active" sorting. Both of which are "algorithms".
It's a lot more simple of an algorithm, and doesn't intentionally push specific topics, but if you open https://lemmy.world/ anonymously, you'll see a default "All/Active" feed which is sorted by engagement.
Google - let's put AI into everything and force it on our users, they'll love it!!!
Also Google - Stop using AI for your content, our users hate it!!!