Hi Aaron-S,
Thanks for posting in Apple Support Communities.
We understand you want to create a custom Focus and prevent your Mac from sleeping. You can create the custom Focus, but you would need to specify your sleep/wake settings for your Mac. This cannot be linked to your specific Focus.
Learn more about creating a custom Focus with Set up a Focus on Mac - Apple Support.
Set your Mac to go to sleep after inactivity
1. On your Mac, choose Apple menu 
> System Settings, then click Lock Screen 
in the sidebar. (You may need to scroll down.)
2. Do any of the following:
* Click the pop-up menu next to “Turn display off on battery when inactive” on the right, then choose an option.
* Click the pop-up menu next to “Turn display off on power adapter when inactive” on the right, then choose an option.
Specify sleep and wake settings for a Mac laptop
1. On your Mac, choose Apple menu > System Settings, then click Battery 
in the sidebar. (You may need to scroll down.)
2. Click Options on the right, then do any of the following:
* Put hard disks to sleep: Turn on “Put hard disks to sleep when possible.”
* Update your system while it’s asleep: Click the pop-up menu next to Enable Power Nap, then choose an option.
* See What is Power Nap?
* Allow your Mac to wake briefly so users can access shared services (if applicable): Click the pop-up menu next to “Wake for network access,” then choose an option.
* See Share your Mac resources when it’s in sleep.
You can find these details and more in Set sleep and wake settings for your Mac - Apple Support.
Regards.
