I found a Netgear Orbi RBR50 v.1 (the one with the USB) for cheap. I don't intend to use it with a satellite (the RBS50), and usually will just have wired internet. I see this device in the supported devices, but there's no install page.
NETGEAR RBR50 [22.03.2] (https://openwrt.org/toh/hwdata/netgear/netgear_rbr50)
While I've used linux for a long time, I haven't experimented with OpenWRT. Anyone have any suggestions about where I might go to get started with this device?
I used Tftp from my laptop to pull the factory firmware,
The wiki page states using OEM GUI (which didn’t work for me), or a utility called nmrpflash - https://github.com/jclehner/nmrpflash.
The git commit always contains flashing instructions, unless you're looking at a very old device.
That solves it for flashing openwrt, thank you, @Stevec9000 and @Borromini . 
I'm also going to need to make a backup of the stock firmware. These seem to be the instructions:
Generic NOR Backup
NAND Specific Tools (nanddump and nandwrite)
For nanddump, how do I find a cross-compiled version, and get it onto the device?
I haven’t gone very deep, just starting with owrt myself. I’m using it in a home lab while I play with Pfsense.
There is an owrt package called nand-utils that can installed on the router.
In luci, navigate to software, update list, and filter for nand.
Thanks, but that's for when you already have owrt installed. I'm looking to backup the stock fw.
Sorry I misunderstood. I have yet to set up my own dev environment for this.
Do you really need the fw from the router itself? Can’t you get it from NG.? You can use the gui to save your config, install owrt, and backup the boot loader partition.
Again, I apologize for being little help.
There's no advantage to doing that; reinstalling the OEM firmware will get you all that data back. What you can (and should) do is back up the radio calibration data, bootloader etc. once you installed OpenWrt. Especially calibration data is device specific. OpenWrt will not overwrite any of that, so you can still safely use the NAND utils Stevec9000 talked about after installing OpenWrt.
Ok, thanks. That helped. I'll look into specifics of how to do that once I get owrt on there...
Anyone tried going back to factory image on RBR?
I was able to install openwrt using the web gui of the orbi, I didn't have to change the partition and it booted to openwrt.
I want to go back to stock firmware, I tried both ways, using the gui and nmrpflash, both failed and it boot back to openwrt.
I am not finding any instructions on putting this on my Netgear ORBI RBR50 (and satellite RBS50). Where do I find those? The links take you to GITHUB where you can download a multitude of files - but no instructions on doing this.
Also - can both the RBR50 (router) and RBS50 (satellite) - they were sold as a set RBK50 when I bought them 5+ years ago.
Under installation here, as @Borromini had posted, above.