[OpenWrt Wiki] NETGEAR R8000 Nighthawk
https://openwrt.org/toh/netgear/r8000Installation As of OpenWrt 19.07, the R8000 can be flashed to OpenWrt through the stock web UI. From the 'Firmware Downloads' tab above, download the most recent 'install' build of OpenWrt (as of this writing, openwrt-19.07.1-bcm53xx-netgear-r8000-squashfs.chk) Connect your computer to the router via wired ethernet.
DD-WRT » Router Database
https://dd-wrt.com/support/router-databaseFor users interested in DD-WRT but afraid of flashing a router due to concerns about warranty and bricking, FlashRouters offers pre-flashed routers with recent, stable DD-WRT releases for purchase ... For more up-to-date firmware files, please visit the firmware faq.