Search interest for “beginner motorcycle” is strong because the first bike is the one you drop. In the US market that usually means 300–500 cc, a seat you can flat-foot, and parts at any dealer. Honda Rebel 500, Kawasaki Ninja 400 / Z400, Yamaha MT-03, and Royal Enfield 350/650 twins are the current default answers.
Weight matters more than peak horsepower. A 400 lb standard is easier to park and pick up than a 650 lb cruiser with the same claimed beginner label. ABS is worth paying for on a used bike — it is common on 2010s-and-later Japanese models sold in the US.
New minis (Grom, Z125) teach clutch and traffic but feel small on the interstate. A used 300–500 with service records is the usual better first street bike. Budget for gear, insurance, and a first drop: lever, mirror, and a slider.
Ignore “best beginner motorcycle reddit” threads that push liter bikes. The US used market is full of low-mileage 400s and Rebels. Check title, VIN, and a cold start before you buy.