If taking the high risk of approaching random shady looking vans wear a body cam. They sell them online. Or at least have your cell phone recording video and put it in a shirt pocket to act like a body cam. Live stream if possible in case they take or smash your phone. Others should also be recording you at a distance in case shady person drops you. Give the footage to the local authorities. I personally would also mention to dispatch that due to the dark windows you could not tell if they have a firearm. Other potential advice would depend on the laws of where you reside.
but in the cheaper, but legally grey area, you can usually lookup a plate for a few dollars if you have a "legitimate reason" such as the creep damaged your property or theft. that's a he-said-she-said thing, so ...
https://www.dmv.ca.gov/portal/file/request-for-record-inform...
of course this is USA, California. Other US states are mostly similar.
there are 100s of online sites that are "private detectives" that will run a plate for a slightly larger fee. this may be faster and less grey than diy dmv requests.
if you are a real karen/ken you can post a pic of the van and plate to nextdoor, etc. and make a big post about the creepy van.