OK, so hows this for very definition of FML..........
Did lots of googling, nothing.
Went onto the MSI website and had a look at BIOS' and noticed the latest available was in fact a beta version which just so happened to be installed on my motherboard (MAG Tomahawk WiFi X570). Flashed the latest non-beta BIOS and gave it a try.
Here are the specifics of each try I then performed:
Garuda Dr460 - All GB settings - Prop Drivers - FAIL
Garuda Dr460 - All GB settings - Community Drivers - FAIL
Garuda LXQt - All GB settings - Prop Drivers - FAIL
Garuda LXQt - All GB settings - Community Drivers - FAIL
Pop_OS (for giggles) - All GB settings - FAIL
Manjaro KDE Plasma - All GB settings - Prop Drivers - FAIL
Manjaro KDE Plasma - All GB settings - Community Drivers - FAIL
Manjaro XFCE - All GB settings - Prop Drivers - FAIL
Manjaro XFCE - All GB settings - Community Drivers - FAIL
Then for some reason (frustration), with Manjaro XFCE I got set sick of setting the language so I just smashed enter, so all US settings with Prop drivers....... it only went and worked! Installed Manjaro, updated it, ran various hardware tests, everything good.
So, as I reallllllllly want to use Garuda, re-ran Dr460, all US, prop drivers - and here I am updating this post from within my newly installed OS.
I have no idea 
TL:DR
Don't use BETA BIOS'
Don't set GB language
Profit
Thanks @BluishHumility @SGS for trying. Bizarre one this