how to stop signing in for free apps and updates ?

Are you talking about payment verification? That's completely different:

Create or use your Apple ID without a payment method - https://support.apple.com/HT204034 - "When you use your Apple ID to sign in to the iTunes Store, App Store, or iBooks Store for the first time, you're asked to enter a payment method so that you can purchase items from the store. Follow these steps if you don't want to associate a payment method with your account." - more information: https://discussions.apple.com/thread/8293272?answerId=33067311022#33067311022

If you've got Touch ID on your device, you can enable Touch ID under Settings>Touch ID & Passcode and then use Touch ID for iTunes & App Store purchases (an option under the same Settings pane). Then you would only need to enter in your passcode one more time and then you could use your finger. That seems to be easier. 🙂

If this is on an iOS device : Settings > General > Restrictions > Password Settings > Require Password ('free downloads') 'off'

Was it already 'off', or have you changed it ? If it was already 'off' try toggling it 'on' and back 'off' (you will probably be prompted to enter the account's password for both)