The current "Image-Line FL Studio 20" version has two main EQs, which are Fruity Parametric EQ 1 and Fruity Parametric EQ 2.
Neither of those FL Studio EQs has brickwall filter possibilities, although this might be added in the future.
Izotope Ozone Equalizer comes with a brickwall filter, available in both analog and Digital variations. So if that's what you are trying to replicate, you won't be able to do that with default FL Studio Plugins.
Fruity Parametric 2 currently supports up to 8th Filter Order, allowing it to roll off frequencies at a cut-off point of 48 dB/octave. Therefore, that's nowhere near what a brickwall filter is capable of.