What are the best motherboards for AMD Ryzen 7 9800X3D with USB4 support?

If you don't need PCIe 5.0 right now, I'd suggest looking into an add-in card for USB4 instead of upgrading your whole system. But if you're building a new setup, consider going with one of the X870E motherboards. They offer full functionality across USB, SATA, and PCIe lanes due to their additional chipset. If you don't plan to use any PCIe 5.0 devices, that's fine—PCIe is backwards compatible, and you can configure lane distribution as needed. Otherwise, an X870 (non-E) is a solid choice if you find it at a good price.

Have you considered certified Thunderbolt 4? It's something worth looking into. It has really great compatibility and speed, plus it works with USB4 cables. Just to clarify, if you use a USB4 cable with a USB3 port, it'll only operate at USB3 speeds. So, checking out options that support Thunderbolt might give you more flexibility and speed when transferring files.

Just a heads up, B850 motherboards are also PCIe 5.0 compatible. There are X670E motherboards that support USB4, but they come at a higher price point and also include PCIe 5.0. If you just want USB4, a motherboard that supports the 9800X3D will likely feature PCIe 5.0, which seems to be standard for newer models. The difference in price between the ASUS ROG Strix B850-E Gaming and a budget-friendly X870 (like a $150 Gigabyte model) can be substantial, mainly due to brand and features. If USB4 is your priority, the cheaper Gigabyte X870 Gaming will suit you just fine, or consider the $190 Asus TUF Gaming X870-Plus for extra M.2 slots. Most of these motherboards will perform similarly for your CPU, and the build quality can vary across the board, so don’t worry too much about the brand unless you need special features.