Businesses effectively get Windows for free. As a small user you get it free with your IT purchases, as an enterprise user you get them free with the enterprise licenses for backend servers.
Checking invoice... Nope.
The Microsoft 365 plans now include Windows 10 (Pro or Enterprise) as an upgrade to the OEM Windows license on the box. (Which is why enterprises buy computers with Windows Home installed rather than paying twice.) Prior to that, Windows 10 upgrade was available as an addon to the Office 365 plans.
Server licenses do not include any client licenses. In fact, to access any server requires an additional client license, either a per user or device CAL or an external connector for non-enterprise users. Different subsets of these are bundled in the M365 plans but not all.
This is a simplified explanation. Larger orgs literally have full time people who deal with this stuff. My software vendor has a licensing team dedicated to Microsoft. It's gotten better over the years, but it's still the most convoluted paperwork that I have to deal with every year.