It is a Netgear router, so it likely has the same TFTP recovery flash routine in the bootloader as e.g. WNDR3700v1 and R7800 etc. You should be able to recover the router by flashing a new "factory" image with that TFTP tool.
(WNDR3700 v4 is different than those routers I mentioned, but Netgear has been pretty consistent with the bootloader)
Reverse to OEM firmware using nmrpflash, than flash openwrt 21.02 factory. Do not upgrade from 19.07, the partition layout has changed. Once done this router works fine under 21.02.
Yes many answers to this issue have been done weeks ago.
Yes it's only upgrading from 19.07 that cause issue as the partitions layout has changed. Flash directly a 21.02 factory image with TFTP or from Netgear GUI. That works well. Once done, you can safely upgrade to newer releases. I have flashed a new build yesterday.