Well... I would like to refresh this thread because I was fighting with this issue yesterday. I've read some posts about this issue on TenForums and outside forum and some people said "you need to upgrade microsoft store first", "you need to do it from administrator account", etc. but in my case, Windows 10 Home S upgraded to the latest version and I couldn't switch from S mode in any way. Uninstalling updates, resetting Windows to factory state, recovering from recovery didn't help anything. I've had to make Microsoft account, switch from S mode then I've had to delete this account from the operating system then after login to my microsoft account through the website I've had to delete this device (notebook) from my devices list. This computer was not for me, it was for one of our ciustomers so I didn't want to left any of my microsoft's account informations on it. Why did you buy notebook with Windows 10 S version you will ask? Well... my boss made a mistake making the order so...
In addition... I'd like to mention that if you have a business Microsoft's account then you won't be able to use that account to login to MS account on Windows 10 S (Home, Pro, whatever) because I've tried it.

FIRST OFF, THANK you Shawn for this helpful post,

However there's another twist in between steps 4 or 5 where I was faced with the somewhat ambiguous choice of "Use this Account everywhere on your device" which I did not want.

So I chose the small print choice at lower left of "Microsoft apps only". Which at this point I'm not sure if I wanted that either.

Can I run the S mode switch out again and just close the popup at the top right X ?

( I login on all my devices with a local acct. I log in to MS only when I have to like to switch out of S mode etc )

Brink said:

Hello, Closing the popup may cancel the S mode switch. The popup would be normal since you are only signed in with a local account.

Ok, so you're saying the "Use this Account everywhere on your device" was referring to my Local Login Profile and not the Microsoft account I was logged into when this popped up, correct?

And if that's correct, where in settings should I look to rectify this totally to my local login and not just for "Microsoft Apps only" which I previously clicked?

Brink said:

It's referring to the Microsoft account. It's basically asking if you want to switch from signing in to Windows with your local account to the Microsoft account instead.

Ok, that's what I originally thought it meant and I definitely do not want that, so why is my only other option to choose for "Microsoft Apps only"? Or more pertinent what exactly does that mean?
In other words all I want is to get rid of S-mode. Why is it giving me only two options, which neither sound like anything I would want or need?

Brink said:

Poorly worded to make (trick) you into using a Microsoft account.

Thanks for the reply, yes with your help I see that now. Additionally the lower left small print option you still have to sign in to Microsoft to use their purchased Apps. I was hoping for a 3rd option but alas I wasn't yet robotically woke enough to realize that option has been dropped. I hear that old 70s song "For what it's worth" again. Something happening here, but this time it's becoming more clear everyday. But fortunately I don't use any of those apps.