You can subtract the members of one list from another by combining the "On Saved List (Name)" filter with the Remove records group in the query builder.
How it works
The query builder supports three group types:
Narrow records — adds an AND condition (keeps only people who match)
Add records — adds an OR condition (includes additional people)
Remove records — adds an AND NOT condition (drops people who match)
The "On Saved List (Name)" filter matches people who are members of a named list. Putting that filter inside a Remove records group excludes those people from your results.
Steps
Open the list you want to filter, or start a new search on the People page.
Build or confirm the criteria that define your starting set of contacts.
Click Remove records to add a new filter group below your existing rules.
Inside that group, add a filter and choose On Saved List (Name) from the field picker (under the "Saved Lists" section).
Set the operator to is and select the list whose members you want to exclude.
Save the result as a new list if you want to reuse it.
Anyone who appears in the excluded list will not appear in the results, even if they would otherwise match the rest of your criteria.
Notes
This works with both static and dynamic lists as the exclusion source.
If your exclusion list is dynamic, the excluded members are recalculated each time the filter runs.
You can add more than one Remove records group to exclude multiple lists at once.
To exclude contacts who are on *any* of several lists, add each list as a separate filter inside the same Remove records group using the OR combinator, or add multiple Remove records groups.