There's a Vantage Service update that has caused an issue with the App itself and disables all the Legion features.
To get around this you need to uninstall BOTH Lenovo Vantage and Lenovo Vantage Services via Installed Apps which you will find in Windows Settings.
Then reinstall Vantage from the Microsoft Store and crucially leave it open. Do NOT close the App, just minimise it and you will be able to control the Legion features again properly.
If you make the mistake of closing the App instead of minimising it, you will have to do all this again.
An alternative for now which I wouldn't normally personally recommend is to use the non-official Legion Toolkit App instead.