I'm no expert, but maybe this can help.
Here's what I did with mine when I thought I bricked it. Keep in mind that I had a micro-USB to USB OTG cable. (costs less than $5)
Mine was bootloader unlocked, s-on but with hboot 1.55 or 1.54.
1. install TWRP recovery (openrecovery-twrp-18.104.22.168-m7.img) using fastboot.
2. Boot into TWRP recovery, then using OTG cable, mount a USB flash drive that has a installable zip image of the whole thing. I just used one from here:
I got the "Download stock odexed 4.19.401.8" since I wanted to return it to stock like so I can return it.
I flashed it with that, and it would reboot into stock-like Android. I still had a bootloader from GoogleExperience version, and I accidentally did S-on before fixing these so I was screwed.
Anyways, that's how I got mine back to working state. After that, I couldn't get S-off (hboot 1.54) no matter what even using Rumrunner. Trying to get S-off again, I had to reflash the kernel with some other custom kernel, and then was able to do rumrunner to get s-off again. From that point, everything was easy, and I was able to reinstall real AT&T stock android using their RUU exe file. After that it installs OTA updates too.