can i give root access to an app without root my phone?

No you can't.

Some apps like Greenify permit you to gain more functionality using adb commands (e.g. see this for Greenify). My device is presently not rooted but I use Greenify powered by these commands and it works well

This is not as powerful as root access but much better compared to vanilla version

These adb commands are not available for all apps as the developer needs to cater for this. It's better to search for alternative apps that facilitate this and use them instead

Aside, some other apps that have this are Wakelock Detector Lite, Force Doze, Macrodroid (these are the ones I use )