If you were using the Windows Key and just started typing, the search field really isn't present until you start typing. My guess is that something has changed about when Windows 10 exposes whatever it is that it exposes to the screen reader to get it to announce the search field. You can still hit Windows Key and just start typing immediately.
You also have the option of displaying the actual Windows Search button in the taskbar and using it instead to launch your search. If you have focus on the taskbar itself and bring up the context menu you should have the Search option, and when activated it will give you a choice of two items: Hidden and show search icon. That way if you activate the search button (which is what the icon is used on) you'll know you've got focus on the Windows search edit box.
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
A man's worst difficulties begin when he is able to do as he likes.
~ Thomas H. Huxley (1876)