My Local Account changed to a MS Account automatically

Is the user name you use for your local account unrelated to what you use for your MS account?
I suggest you make quite sure which kind of account you are using.
How to Tell if Local Account or Microsoft Account in Windows 10

See:
Switch to Microsoft Account in Windows 10
- and you should see it would be hard to conceive of how a genuine local account can magically change without you entering the appropriate user name and password in the appropriate places.

Again, if it's only a local account, nothing should be synched using a MS account by definition.

See:
Enable or Disable Sync Microsoft Edge Settings in Windows 10
Turn On or Off Sync Microsoft Edge Settings across Windows 10 Devices
from the searchable Tutorial section (do feel free to have a look yourself) to disable Edge syncing.

More related tutorials linked below the main text.

win10freak said:

I cleaned installed my Windows 10 machine and My Local Account changed to a MS Account automatically right after I signed in to my Microsoft accounts like Outlook and Edge.
Next time I setup my machine, how can I avoid this from happening again....

No, not automatically. You were being fooled into asking to make the switch to a Microsoft account.

To use the Store or OneDrive it will first ask you to sign in with your MS account. The box for signing in to your MS account innocently asks if you'd like to use this account everywhere, with a big friendly blue button labelled 'Next' for you to click. In very small print on the left is a link that says 'Microsoft apps only'. Click Next and you suddenly find your Windows Local account has turned into a Microsoft account. To keep your local account you must click 'Microsoft apps only'.

win10freak said:

How can I generate that window prompt just to see what happens?

Try signing in to the Store.

win10freak said:

I think it's late for doing this because under Settings/Accounts/Email and accounts I already have the option set as Microsoft Apps Can Sign me In.

You can remove your MS Account, click on your account name and there should be a Remove button. Then it would be back to never having signed in with it at all.

Never mind....

I got that window prompt after signing out and signing back into the MS Store.
And I also clicked on the Sign in to MS apps only link then clicked on Next.

All good now.

Also, I did a test with Edge by deleting the Edge User Data under my user profile directory and when I opened up Edge, this time I selected the Sign Out option then unchecked settings related to syncing, then i after that I selected to Continue Without my Data. It works. Next time I will keep this in mind.

Its strange, because when I first signed into my MS Account using the Outlook app, I never even seen that window prompt before. Please explain the reason.

win10freak said:

Its strange, because when I first signed into my MS Account using the Outlook app, I never even seen that window prompt before. Please explain the reason.

That I can't do, I have never used the Outlook app I'm afraid.