This is the manufacturer recommended way to cut holes in Hardi Board concrete backer board. There are of course other ways, but manufacturer recommendations are usually there for a reason.

Link to the classic utility knife $14 for 2:
https://amzn.to/3LfOkWl

Fresh utility knife blades $5.50 for 10:
https://amzn.to/3qrXLIk

Here's an inexpensive carbide tip scoring blade $16:
https://amzn.to/3qnkEN8