First google link that looked reasonable. I have not followed this. But I bet it will work.
homeassistant
Home Assistant is open source home automation that puts local control and privacy first. Powered by a worldwide community of tinkerers and DIY enthusiasts. Perfect to run on a Raspberry Pi or a local server. Available for free at home-assistant.io
I know HomeAssistant can run on my NAS, so buying more hardware seems like overkill
I have never seen nor used a WD MyCloud, but if you know that an upgrade allowed for HA to run (I presume in Docker), then how about just wiping whatever OS is on the NAS and installing a Linix distro, then moving up from there?
A few use TrueNAS to run HA in docker, but a few quick searches shows that won't work on your hardware.
Probably a lot more work than you were intending, but should simplify the future for that NAS and prevent any kludgy workarounds from trapping you again in the future.
And... I presume you have a backup of everything on that NAS 😉
You need something like a raspberry or a small computer to run home assistant 24/7 and you also need a zigbee coordinator (to be able to use your ZigBee devices) like sonoff CC2652P or conbee 3 (others are available). Install home assistant, and learn how to manage/customise as you wish.
Home assistant is great but it's not a plug and play option, settings basics stuff isn't complicated but you will have a learning curve to be able to do more (depending of knowledge you already have)
I was hoping someone could tell me how to get it to run on my NAS. I know people use Docker for it, but I don't know which one or how to? I do have a Sonoff Dongle.
Oh! Ok. Maybe you can try this https://community.home-assistant.io/t/installing-home-assistant-on-wd-mycloudex2ultra/530270
Thank you so much for the time and effort you're putting into helping me, I really appreciate it. Unfortunately though, that's not for the original MyCloud. My version didn't get the update to version 5 of the operating system, which is step one of the instructions you linked, hence the conundrum I'm in and subsequent plea for help. It was kind of a hail Mary, hoping for a miracle.
Unless you can find an alternative firmware that can run docker, I don't see any other options. Wish you luck