Can you connect two or more alarm boards together to create more zones?

How to Expand Your Alarm System by Connecting Multiple Boards Together.

Yes, you can. The boards can be infinitely expandable, so if you wanted 24 zones, you would purchase 2 x Pro boards which come as standard with 12 zones each. If you wanted 48 zones, you would purchase 4 x Pro boards.

The boards would then communicate independently but work together in Home Assistant, SmartThings, Hubitat, or whatever platform you use.

Here's an article that discusses the topic of adding more zones.