It says it twice: "nominal" and "rated". Both mean the rating the capacitor is sold with. No confusion here. This is better than usual, often the datasheets just talk about "capacitance", but values like "22uF MLCC" are the giveaway: they must be nominal ratings. If it was an actual value, it would say a round number like 20uF for example.
Except, of course, this holds a hidden assumption! As they nowhere tell the actual amount of capacitance required, you need to assume they used some "typical" capacitor available on the market.
But typical high-capacitance MLCCs, that would get used in typical converters, under typical DC bias, vary from maybe 15% to maybe 60% of rated capacitance! It's quite a range of variation. Also note even avoiding just Y5V is not enough. A decently rated X7R part may well drop into 20% under bias. You need to have the curves, or failing that, assume based on ratio of package volume / (Vbias * Cnominal), in other words, "too good to be true" energy density realistically means it is not true.
I would just assume C_actual is 40% of that rating. So 22uF nominal = 9uF actual. So leave the worst offender caps that drop down to 15% under your DC bias on the distributor's shelf, but OTOH, don't waste time trying to find those that perform best-on-the-market or are in massive package sizes, because low inductance (small package) also matters.