Having an F-Droid version that costs nothing but has a donation link and a Play Store version that is not free is a common monetization pattern for open source projects on Android. See also:

https://play.google.com/store/apps/details?id=net.gcompris.f... vs. https://f-droid.org/packages/net.gcompris.full

https://play.google.com/store/apps/details?id=com.mkulesh.mi... vs. https://f-droid.org/packages/com.mkulesh.micromath.plus

When Google gives me free Play Store credit, I often "donate" it this way.

The problem is this is a very inefficient donation: A third of it goes to a greedy for-profit corporation that actively causes societal harm.

If you're using Play Store credit for it, sure, nobody but Google is paying the bill. But for everyone else who buys the app, it's a pretty poor donation method.

> The problem is this is a very inefficient donation:

How is it inefficient? Google gave me that money for free, and I sent 70% of it to the project and 30% back to Google.

> A third of it goes to a greedy for-profit corporation that actively causes societal harm.

Also wrong. Less than a third of it goes to anybody but the app publisher. Of the 30% that doesn't go to the app publisher, some portion goes to the payment processor (usually card processor or mobile service provider, only Google if you pay with credits).

> But for everyone else who buys the app, it's a pretty poor donation method.

They can also donate via F-Droid, as I showed in my post. The fact that it costs anything at all on the Play Store encourages users to get the app from the author directly or from F-Droid, both of which give the app away for free and can show preferred donation links. They get to benefit from wide distribution and discovery via Play Store and better monetization via donation links. Compare to iOS, where the open source authors are screwed.