Conventional dynamical decoupling employs pulse sequences whose microwave implementation relies on the rotating-wave approximation (RWA), which constrains the driving strength to remain much smaller than the qubit energy-level splitting. This requirement fundamentally limits pulse speed and detection bandwidth, particularly in systems with small level splittings. Here we develop a Floquet-engineered dynamical decoupling framework that operates beyond the RWA, which can simultaneously achieve high-fidelity decoupling, faster spin manipulation, and enhanced robustness under strong driving. Based on these pulses, we construct Floquet DD sequences that maintain decoupling performance while substantially extending the detectable AC magnetic-field frequency range. Numerical simulations by using nitrogen-vacancy centers, demonstrate reliable quantum sensing in regimes inaccessible to conventional RWA-based schemes, with the detection bandwidth scaling directly with the achievable Rabi frequency. Our results establish Floquet-based dynamical decoupling as a general strategy for broadband quantum sensing in strongly driven two-level systems.