After hours of trying to figure out what the problem was, I managed to get my left over NZXT Hue+ light strips working perfectly with the WS281x LED Status plugin made by @Charlie_Powell. The reason it wasn't working initially is because I had already tried other plugins like 'RGB Status' and even though they were uninstalled there were still leftover parameters in the boot config.txt file (such as gpu_mem, core_freq, etc). I restored the config.txt file to it's default state (bit more googling) by deleting all non-default entires, some of which were likely still required by 'WS281x LED Status' but I did it anyway. But luckily @Charlie_Powell must have thought of this and when the plugin boots up again it will prompt you to set the required entires back in config.txt.
So for anyone struggling to get WS2812 (or any other LED strips) working properly and trying heaps of different plugins without them just glitching, staying white, etc - give that config.txt file a damn good enema and use the WS281x LED Status plugin.
I now have my NZXT Hue+ light strip (appears to be 5 Volt - printed on the strip input +ve port) running perfectly from the 5V power pins on the Pi (Pi 4B 8GB) and using GPIO 10 for the light data. No clunky separate power supply + cables nonsense - a clean installation which gives heaps of light for my timelapses and remote monitoring.