So I'm comfortable labeling OER as "openwashing", given the current draconian copyright environment.
In addition to OpenStax and Khan Academy, I can recommend MIT OCW and, if it's legal in your country, downloading textbooks from Library Genesis.
However, surely Gates is correct when he says, "Courses should be created by educators and subject-matter experts, supplemented with professional development, and regularly improved with feedback from the teachers who use them."
It's probably also worth mentioning Project Gutenberg and the Internet Archive, although you probably won't find an up-to-date textbook for a class in them unless you're studying Classical Greek or something. And no lesson plans.
But there's nothing wrong with profits. Profits are great! My concern is teachers and students potentially being put into a very unprofitable situation where they become dependent on oer-prj.com, perhaps when their angel funding runs out. Under current copyright law they wouldn't have the right to keep making copies of the PDFs they can download today, unless those materials are explicitly licensed to protect them from such rugpulls; they'd have to either pay whatever price oer-prj.com decides to charge, or switch lesson plans and textbooks with, potentially, no warning. Possibly no price will be sufficient if the rugpull is part of a US sanctions package against their country.
Legal protection from such scams is central to the usual definition of "Open Educational Resources", as articulated for example by UNESCO: "Open Educational Resources (OER) are learning, teaching and research materials in any format and medium that reside in the public domain or are under copyright that have been released under an open license, that permit no-cost access, re-use, re-purpose, adaptation and redistribution by others." https://www.unesco.org/en/communication-information/open-sol...
The so-called "OER project" Gates is funding fails to meet that bar.
And that's slimy.
Added: the Gates Foundation did (and may still for all I know) provide funding to some OER projects 10+ years ago, also to Creative Commons on the idea that organization was infrastructure for OER or something like that. I'm not really suprised if they've focused on getting schools to adopt whatever they are funding, really open or not, since then; it sounds like they've had some success. If there's a trove of under-exploited openly licensed educational videos linked above based on that engagement, and/or based on YouTube adding the ability to opt into CC-BY-3.0 licensing sometime before then, I'm mildly satisifed.