https://wccftech.com/amd-ryzen-threadripper-strx4-tr4-socket-layout-detailed/

The pin layout of AMD's Ryzen Threadripper sTRX4 and TR4 sockets has been detailed by Hwbattle who have compiled a full pin configuration map for the two sockets. It looks like with the updated pin map, we shouldn't expect any kind of compatibility with the older TR4 socket-based CPUs even if the sockets look visually identical.

Since the start of the 3rd Gen Ryzen Threadripper processor rumors, we have been hearing that the new TRX40 platform won't support older processors. This was confirmed a few days ago with the announcement of 3rd Generation Ryzen Threadripper processors and the respective TRX40 series motherboards. Motherboard manufacturers clearly mentioned that their TRX40 series are compatible only with the 3rd Gen Threadripper series and not the older lineup.