Google is not the payment processor. This is about the app including a link to a donation page on opencollective.com.
Other 501(c)(6) organizations you might have heard of include the Linux Foundation and the Rust Foundation.
Other 501(c)(6) organizations you might have heard of include the Linux Foundation and the Rust Foundation.
Indeed, those are structured as corporate-funded consortiums of exactly the type you'd be very suspicious of if, say, your kernel or compiler logs started stuffing a donation link into the stream!
Note that GNU software does historically mention donations (not in the logs AFAIK), and indeed the FSF is a 501(c)(3).
"Phone apps" is irrelevant, because again, Anki was not taking donations via their app but rather via a link to OpenCollective, a separate website.
So the remaining part of your question:
> Do LF and Rust solicit individual donations (at all, really)?
Yep, the Linux Foundation has a PayPal donate button (with a simple note to U.S. taxpayers that it's not deductible): https://www.linuxfoundation.org/about/donate
...Irrelevant? That's the whole point. "Taking donation via a separate website (emphasis in original)" is explicitly dissallowed in the Play Store (and App Store on iOS)! There happens to be an exception carved out for federally-registered charities. But no, you don't get to just hold out a link to a tip jar.
Does this link count as a charity? No, per the structure of federal tax law. Also no, per the set of rules of the app store it's trying to be listed on. Should it count? Well, maybe I guess? Open source projects are like charities in some cases. We should all want to support them. But doing it like this, through a middle-man organization that isn't a charity, just plain smells like fraud to me. Who's doing the auditing that this is just supporting development and not profit centers? Is the IRS doing it? Not as far as I can see.
Then why did you throw "(or at all, really)" into your question? For the zinger, even though you now think it's irrelevant?