I am using android 9 on Samsung device, is there is any way to add widgets available in home screen on lock screen (on rooted phone) and able to use them without opening lock screen ?
It is possible with edxposed and GravityBox module.
Note: Gravitybox doesn't go well with heavily modded UI like Samsung, Huawei etc. So check the XDA thread, for your device specific issues and fixes. It may or not work.
Installation instructions for EdXposed (though it's for Android 10, it is applicable for Android 9 too as far as installation of EdXposed is concerned). Note that some Samsung, Huawei devices also have issues in installing EdXposed and you may need to try alternatives (YAHFA /Sandhook)
Download & install GravityBox from XDA thread
In the GravityBox menu Lockscreen (first menu option) →Shortcuts, select the apps you want displayed on lock screen
Test by tapping the widget, opening the screen lock. Your application should be launched. Unlike Phone and Camera options that are usually found on lock screen and can be launched directly without unlocking device, you need to unlock device to access the app launch. If you want the behavior to mimic phone /camera, you will need to disable lock screen