The same part of the software supplies both functions, thus why they are enabled/disabled as one.
When you do not have a URLF license (i.e. because you have an NGFW license), then you cannot use functions that rely on URLF.
Specifically, that means you cannot use URL Filtering categories in your rulebase.
You can still use App Control categories or custom URLs in application definitions, as that will be covered by App Control (covered by NGFW).
Note this is exactly how it works on non-SMB appliances as well.