I have a smart group with this, linked to a policy that pops up a message top say 'less than 20GB free' adjust accordingly... same will work for an advance search..

Criteria - Boot Drive Available MB - less than - 20000

I'm guessing that big Home folders are causing problems for other users, I ran into this and built a Smart Group where is a Member of the Labs Macs and Boot Drive Percentage Full > 95% for triggering an automated clean up, deleted all Home folders apart from the logged in user.

You could do it with a search

And Boot Drive Available for targeting macOS upgrades

Unfortunately Boot Drive is not quite reliable indicator anymore.

I would suggest create Extension Attribute (input type - script, data type - integer) and use something like this to check the percentage of Data volume used (you can put there any other volume if you want):

#!/bin/sh
free=`df -m /System/Volumes/Data/ | awk '{getline; print $5}'| sed 's/%//'`
echo "<result>"${free}"</result>"

You can create a smart group and scope it then.