Short answer is probably not much. Both Fairfax and Prince William public safety are P25- which is the bread and butter for the scanner.
The other options are different digital modes. If you look at the radio reference database, drill down to the state and then the county, you can see who is listed and what type of mode they use under “mode” or “type” on the right hand side.
DMR is listed a few times, but stuff like trash pickup, taxis industry and maybe some school stuff. I didn’t see any NXDN. And ProVoice was not widely used (except where I live), but it’s on its way out, if not already out of most places. So really no point in that one either. Oh- ham radio does use different modes at times. You may find DMR or nxdn at times on the ham bands if you are looking.