I'm no fan of Windows myself, but I find this a fairly bad policy. If nothing else - what's not used is not tested. And if you expect any real population of users to be using Windows machines with your products, you should have developers/PMs/QA/support interacting with your products using Windows machines. I see this as: We're saving a bit of money and making ITs life easier, and in exchange users will get a worse p…
Gitlab is essentially a website, and Microsoft Edge is just Chrome. I think there isn't any reason to test on windows anymore.
The browser is wired into the OS in real ways, and they matter. Everything from "How does the os manage passwords" or "how are system notifications presented" or "How much screen real estate do I have have on a given window size (scrollbars...)" to subtle differences in how the network stack behaves, or how windows are rendered.
Hell, I can list about 20 differences just off the top of my head - and a damn good part of that is because I've been forced to pay attention to each of those platforms. Which clearly you have not...
I read your comment as "I only use a mac, and I don't understand".