how to disable system apps without root? How to disable system apps without root?

My phone model is vivo x5 max+ and android 4.4.4

I have tried Debloater but it failed to connect (I am sure I've allowed USB debugging).
Provided that you've adb setup and functioning, use this command in a console:

adb shell pm block PACKAGE              # for Android Kitkat
adb shell pm hide PACKAGE               # for Android Lollipop
adb shell pm uninstall --user 0 PACKAGE # for Android Marshmallow and Nougat. This is bit tricky. Some reports its result positive, while others, negative. Also note that, later, you cannot restore the app here. It can only be reinstalled again. 
adb shell pm disable-user --user 0 PACKAGE # tested on Android Nougat and Oreo. Might work on earlier versions as well. 


Replace PACKAGE with the package name of the app. To know the package name, try any app inspector type app from Play Store, such as App Detective, AppXplore, Elixir 2, etc. 

The changes should take place immediately, otherwise, try rebooting the device. 

Note: stock ROM implementations by some OEMs, such as Xiaomi and Panasonic, do not permit the aforesaid commands to be used without more elevated privilege, and thus, throws a permission/privilege related error. 

Revision made wrt to info received from Prahlad Yeri in the comments.