Firm and slice: Freeze the beef top round 1-2 hours, until firm at the edges. Trim away all visible fat and silverskin, then slice into strips no thicker than 1/4 inch, with the grain for chewy jerky or across it for tender.
Marinate: Whisk the soy sauce, Worcestershire sauce, brown-sugar-style sweetener, liquid smoke, garlic powder, onion powder, coarse black pepper, smoked paprika and red pepper flakes together. Add the strips to a large zip-top bag, pour over the marinade, press out the air and refrigerate 12-24 hours, turning occasionally.
Dry the surface: Lift the strips out and press them between thick layers of paper towels until the surface is dry to the touch.
Arrange: Lay the strips directly on the oven racks with at least 1/2 inch between pieces, none touching, and slide a foil-lined sheet pan onto the bottom rack to catch drips.
Heat step: Bake at 300°F for 10 minutes. This brings the meat to the 160°F the USDA requires; drying temperatures alone never reach it.
Dry: Reduce to the oven’s lowest setting, usually 170°F, and prop the door open about 2 inches with a wooden spoon handle. Dry 4-6 hours, rotating the racks once, switching on the convection fan after the first 30 minutes if you have one.
Bend test: Cool a strip for 5 minutes, then bend it. It should crack and show white stress lines without snapping in two. Pull pieces individually as they pass.
Cool: Spread on a wire rack until completely at room temperature, about 1 hour, before storing. Warm jerky traps steam, and that condensation grows mold.