AMD has been making ARM chips for a long time (they bought Xilinx and have been an ARM licensee for forever). This is just their first APU (graphics plus cpu) with an ARM core as the CPU.
https://www.amd.com/en/products/adaptive-socs-and-fpgas/soc....
Maybe it would be better for them to enter the Risc-V market. My working thesis is that SoftBank had milked the Arm cow dry. That is why they took it public to pawn the dregs off onto the retail investor. Paying for an Arm license is wasted money and akin to paying for an OS these days.
This is a "why not both" strategy: ARM has the market share whereas the RISC-V ecosystem is still being built up. Once you have a RISC based chip, it's not nearly as much work to change to another RISC ISA.