The way I do it in my SaaS app is there is an "attributions" page. On it I have a list of all OSS software I've used in both frontend and backend.
You probably already knew this, I don't mean to point out the obvious. I am just confused by your comment, and others like it that frequently come up on HN these days. People saying or implying that there is something unfair about using open source software under the license terms that its developers have chosen to release it.
If the OSS developers want to generate revenue, there are plenty of paths they can follow.