Review on 🔩 Magic&Shell M.2 Support Standoff Screw SSD Mounting Kit for Asus Motherboard & M.2 Drives - Easy Installation with Hex Nut Standoff Spacers, Phillip Head Screws, and Screwdriver - Includes Anchor by Anthony Robichaud

This is what you need. My Asus Tuf B350 didn't have a gap, and while you can screw in an M.2 drive without it, it's bent, not perfect, and will likely run hotter since the air gap to the motherboard is as small as intended. There are many things in this kit that you won't need for this build, but keep them for others as these are very specific parts and not easy to find locally, especially here.