Leviton smart switch DH6HD-1BZ, pulling power from existing switch/receptacle

Going to be installing under cabinet lighting and adding a Leviton smart dimmer (model in the title) as well as replacing the switch for my existing sink light with a standard (non dimming) Leviton smart switch. Currently there is a switch for the existing sink light and a receptacle. Plan is to pull power from either the existing switch or receptacle for the new Leviton switch for the under cabinet lights. Basically, I’m going from a 2 gang panel with switch and receptacle to a 3 gang with 2 switches and 1 receptacle and need to figure out how to power the new switch. I have no issues installing these particular switches as I’ve installed several around my house (both single pole and 3-way) without much drama. But I have not had to add a switch (not just replace an existing one) that I’ll need to pull power from another switch/receptacle. So not quite sure how that will work. Thoughts, tips, tricks, etc. are GREATLY appreciated.

Here are the instructions for the dimmer model for reference.