Apple - How can I enable the "back" button of a Razer mouse?

I made an open-source macOS utility called SensibleSideButtons that turns the side buttons on any generic mouse into universal navigation buttons. The application runs in your menu bar so you don't have to install any extra drivers. My approach is to bind the buttons to virtual left and right three-finger swipe gestures, which offers several benefits over the usual approach of binding the buttons to ⌘ + [ and ⌘ + ]: almost universal adoption across the OS (including Xcode), avoidance of destructive behavior, no menu bar blink or annoying noises, and commands only sent to the specific window under your cursor. The only requirement is that your side buttons emit standard M4 and M5 events, which most mice do.

This is possible on Mac OS using Razer Synapse.

Open Razer Synapse, select the button you wish to configure. In the window that pops up, under "button assignment", select "shortcuts". Then, assign the desired shortcut, such as back or forwards.

If there is no such preferences in Razer preferences then you may try USB Overdrive to assign the button to an action.