Would be nice but alas: No, that is not possible currently.
depends; if you want to have the max() function, then that’s not possible directly in an XPath constraint.
In that case a Datasource microflow with a list return will be the solution for you.
Though if you want to have a list where a certain value must not exceed a maximum value, then it can be expressed using;[Entity1_Entity2/Entity2/Attribute <= MaxValue]