FWIW, I second @hnyman's advice to post your flashing commands and outputs.
In one of your past posts, you wrote:
I also suspect this flashing process (and likely the others you've tried) are resulting in the boot loop. I did see other forum members say that they have flashed openwrt directly from the netgear www interface on the r7800. It may be that this no longer works...
Since you've tried several flashing methods and to make it easier for others to help you, I'd suggest you try the following flashing "workflow":
To tftp flash either a netgear or an openwrt factory image for both items 1 & 2 below, follow @hnyman's instructions here. (Post the commands you use to flash and their outputs.)
- tftp flash a netgear stock image (briefly verify that it boots and functions)
- tftp flash an openwrt factory image over the netgear image (I'd suggest the lastest stable 18.06.5 factory image: netgear_r7800-squashfs-factory.img) (i.e. do not use any www interface and do not use a "sysupgrade," or "initramfs" image).
- post the boot log from the serial interface if you get a boot loop.
Lastly, from the year or so I've spent with openwrt using an ipq806x device similar to the r7800, my observation is @hnyman is one of only a handful of experienced forum members that helps (new) users with the r7800... be patient).
HTH