Sorry, but this seems like quite a bad take. There's aspects of this I can 100% agree with and others that smack of opinion with a lack of research or knowledge.
You make the assertion that "some freeloaders just use this stuff and don't contribute anything back. Many might not even realize that they're doing it. Apple's macOS is built on a basis of open source. Android is too, and ChromeOS". When it comes to Linux and hardware support, we are primarily talking about kernel level development. This is an area that I'm fairly familiar with. Let's just take a look at the development statistics for a few of the last kernel development cycles (data from LWN):
6.0: Google, 85886 lines changed, 5.4% of total, 4th overall in this metric.
5.19: Google, 30767 lines changed, 2.5% of total, 8th overall in this metric.
5.18: Google, 103801 lines changed, 8.8% of total, 3rd overall in this metric.
5.17: Google, 24971 lines changed, 4.1% of total, 6th overall in this metric.
Broadly the same looking at changesets.
That also probably misses a tonne of work that they finance in the kernel space alone through outside consultancies (which I know that they do).
I know that their contributions also extend to at least some other FOSS components they use, though I have far less knowledge there as it's not my area of focus. There is probably broad swathes of the Linux ecosystem that they don't contribute to, however there's large portions of the ecosystem that aren't used in the products they create. There certainly are vendors in the FOSS ecosystem that use and contribute nothing back, but (for all their sins) I don't feel it's remotely appropriate to try and paint Google in that light.
(For transparencies sake, I don't work for Google, however I do work at a consultancy that does work for Google so have some awareness of some of the work done for them although I'm not currently involved in it.)