There is no hard and fast rule. Keep in mind that the recommendation is purely looking at your recent training history, and trying to suggest what it thinks is “best”.
That has nothing in mind other than a general goal to increase fitness with an attempt to prevent over-training. Knowing what your actual goals are may lead you to choose harder or easier rides than the “recommended one”.
It’s a nice tool, but it’s not magic and should be altered as the rider sees fit to meet their needs and even preferences.