Many state governments have declared temporary "shelter in place" statutes due to Covid-19 that restrict unnecessary travel by vehicle. I know this will vary by jurisdiction: but generally, is the suspicion of unnecessary travel sufficient probable cause for a traffic stop and questioning the driver and passengers as to the nature of the travel? Is probable cause not necessary under these temporary "shelter in place" statutes?
A reasonable suspicion for a Terry stop has to be based on "specific and articulable facts", and not based just on a hunch. A mere "feeling" that a person may be traveling unnecessarily would not legitimize a stop, but some concrete evidence could. For example, 8 teenagers in a car repeated driving a loop experientially looks like cruising, which is not in the category of necessary travel. 8 70 year olds doing the same is probably about as out of the ordinary, even if you can rationalize it as confused elders.