Best image to reinstall NetHunter on Nexus 7?

I have exhausted what I can find perusing the internet so I figured I'd reach out here to see if anyone can help me. The download on the site is for Marshmallow and even though I have Lollipop I figured I'd give it a shot. I bought this nexus with nethunter already installed and, though it works for the most part, it is old and I can't seem to update it with sudo apt update and sudo apt upgrade. It can't find the repositories that are in sources.list. Does NetHunter use the same repos as Kali? I would imagine not but I'm not sure.
Basically my question is twofold:
1. Should I try changing my repos first and see if that works and, if so, which are the best to add to my list?
2. Which image would work for me to install if I need to reinstall NetHunter to get my Nexus as up-to-speed as possible?

Model: Nexus 7 (wifi)
Android Version: 5.1.1
Kernel Version: 3.1.10-Bricked-v0.591-g0a2e5f6
Build #: LMY47V

I understand it is an older tablet and my options may be limited but I'd like to get it as functional as possible for now. Thanks and any help is greatly appreciated!

Cannot help but have the same problem, so bumping this thread!
(was trying to install drivers for rtl-8812au) which also requires apt update and apt upgrade. Found an old torrent for marshmallow so tried to install that unfortunately settings has stopped working (and a bunch of other errors). Also getting ADB recovery driver errors from the nexus root toolkit, so everything is a bit of a mess.

21.2 requires more system memory to be allocated which doesn't seem to be available. Anyway, my tablet is working, but just in factory mode now. Completely lost nethunter for now. Does anybody have access to the old images?

I'll add my discovery of an older version of Kali
https://build.nethunter.com/release/marshmallow/

That said I managed to install the old version then 2021.2 on top of it in TWRP via a usb drive.

Well it successfully installed but that didn't mean it was actually working.
installing chroot never ends, downloads fine, but hangs on checking the sha512.... (for hours)

The boot image for flo never installs from TWRP with Magisk or SuperSU. Always runs out of room on /system. I guess nobody checks for compatibility anymore...
Nethunter 3.2 wifite cycles through setting adapter into monitor mode but never starts reading. Blugh, might have to call it unless somebody here has some good ideas!

Help please!!!!