The Realtek RTL8261C is an offshoot of the RTL8127 that is power-optimized at 1.65W and designed for WiFi 6/7 routers, cable modems, and more. This is one of the chips Realtek has been aiming to help deliver on lower-cost 10 Gigabit wired networking. The RTL8261D began being promoted by Realtek earlier this calendar year with similar functionality to the RTL8261C.
Now with the upcoming Linux 7.3 kernel cycle, there will be mainline support for these Realtek 10Gb PHYs. This merge to net-next that was pushed on Friday adds the Realtek driver support and is also dependent upon new firmware blobs. The ASIC support is being tacked onto the existing phy-c45 driver code.