The filtering system in ERAS is very flexible. You can create filters on most items, and create complex filters on multiple things. This would include the usual suspects like signals, geo preference, type of medical school, exam scores, etc. Could also include specific schools, countries or states (i.e "show me applicants who have something in their application in my state"), have an impact statement, etc. Can also do full text searching of any of the free entry fields.
Perhaps easier to answer is the opposite -- what cannot be filtered against. We can't filter on past step failures -- I can ask to see who has a current failing result on USMLE/COMLEX, but not if there was a prior failing result. The only way to see that is to open the exam report itself. Can't filter on medical school grades, nor on MSPE quartiles, since those are not field defined. Some companies are working on AI models to process documents and pull out standardized info, my experience playing with them is that they were not good enough at it yet (but that's probably on the cusp, and I didn't reassess last year).