[Sholander]

That's my use case for Odroid N2, CoreElec on USB (SSD) and Android TV (LineageOS) on internal eMMC, which covers all my needs. Both work perfectly...

I have a spare USB SSD I can repurpose to use on my N2+ but despite trawling the CoreElec forums I cannot find the right information to set this up,
maybe I'm putting the wrong words into search but its proving to be a frustrating search.
Would you mind pointing me in the right direction for how to install and boot from CoreElec via USB on the Odroid N2/+ devices please?

Yes I can, but it involves some knowledge and preparation, basically:
Check Petitboot version installed on your N2 -> unplug N2, remove eMMC module, flip SPI switch to left position, power on N2 read info on screen when Petitboot loads
If needed update your Petitboot to version "dev.20220317" -> https://wiki.odroid.com/odroid-n2/os_images/petitboot
Burn Coreelec final 20.5 via Balena Etcher on your SSD.
After that you'll be left with two partitions on your SSD, a small boot partition formatted to Fat32, and the rest formatted in Linux Ext4 (I think) partition. Here comes the tricky part, to be able to use your SSD for your media storage you have to repartition the big Ext4 partition to two, a small one about 32-64Gb for Coreelec Storage, and the rest for your media files. This can be done on a Linux machine, or directly on N2 -> look here how I did it.

My advice is first use an 16-32-64 Gb USB Stick to see how it works without the need to repartition/resize Ext4 partition. Just update Petitboot if needed, and remove eMMC, flip SPI switch to left position, plugin USB stick and power on N2. The installation should go though without any hiccups...