Following @konus ' advice, it is unwise to try to flash directly the latest stable, and furthermore a snapshot on such an old device. You may face partition layout change, kernel size and many other issues that have occured in the meantime since first support.
Simple advice would be to flash an early version of OpenWrt, than upgrade one step at a time. At each step you may face a new problem that requires a change.
Finally when you would have solved all issues and gain experience on how to solve them, you may flash the latest stable. It's not even sure that it runs.
I finally got back to the WNDR4700 at my parents place and updated the bootcmd over serial. 22.03.5 works fine with the new bootcmd however upgrading to 23.05.rc2 does result in a brick. So it looks like the new bootcmd is not enough to get 23.05.rc2 to work unfortunately.