output filter capacitor of a buck regulator behaves as an inductor at the switching frequency. Will the ripples get filtered out?
Does that 100uF cap meet the requirements listed in the LTC3533 datasheet ? I see a low ESR requirement. Note that an ideal 100 uF capacitor would have an equivalent impedance of 1.5 m ohms, that is 0.0015 ohms !!

I dare you to connect that ideal capacitor to the LTC3533 using wires with a resistance less than that 1.5 mohms. Indeed, that is practically impossible.

Conclusion: any 100 uF cap will not behave as 100 uF at 1 MHz, this is to be expected. Just use a capacitor as recommended by the manufacturer and than will be good enough.

If you're worried about 1 MHz (and higher) spurs on the supply then I suggest adding a series choke and a good quality, but much smaller than 100 uF, decoupling capacitor after that choke to filter the supply a bit more. I would use 2 caps like a 1 uF and a 100 pF cap in parallel after the choke.

The choke separates the 100 uF cap from the 2 decoupling caps so the feedback network will not be affected (which is what you want).