The yield on a normal money market fund changes daily. Investors are not notified when the yield changes.
Revolut and Plum offer money market funds at rates that don't change daily. This is to make advertising the product easier. If there is no regulatory obligation to tell investors when a yield changes on a normal daily variable money market funds, then there's probably no regulatory obligation to tell investors when a yield changes on a money market fund where the rate does not change daily.
That said, it is obviously in the consumer's interest that they are notified of these changes and it would be very easy for Revolut to do so.