I'm sure all tech companies use a variety of tech to make sure their products work across user devices.

But their infrastructure sure as hell isn't Windows Server on Azure...

And it's pretty well known that Google uses a lot of Linux internally, even if I'm sure some devs are also on MacOS and Windows for reasons.

you think google/fb production code runs on laptops?

A lot of Google engineers use Chromebooks.

I had https://en.wikipedia.org/wiki/Goobuntu on both a laptop and a desktop, and then replaced the laptop with a https://en.wikipedia.org/wiki/Chromebook_Pixel after those came out because I wanted to see The Future!™

Some of them do.

Most use Mac.