GOOD NEWS!
ASUS have fixed the issue through their latest BIOS update!
For my X570 TUF Gamiung Plus that was version 2407.
After the BIOS was installed and rebooted, there was another screen saying the RGB firmware is being updated. I haven't seen this screen with their previous updates.
One reboot later, the RGB works perfectly. I am using the latest Armoury Crate software to control it and having 0 issues.
Hope it stays like this! I will update if it doesn't.
Anyway guys, you might already know about this, but if you are like me and stopped looking into this issue after finding 0 solutions, then you're in for a treat