The article explores the development of MXene/TiO$_2$ composites through annealing treatment to enhance their electromagnetic (EM) properties. The study demonstrates that by adjusting the annealing temperature, the composites can achieve a balance between EM energy loss and reflection, exhibiting excellent EM absorption and shielding performance. The optimized composites are used to fabricate various EM devices, including an energy conversion device, a strain sensor, and an ultra-wideband (UWB) absorber. Numerical results show that the UWB absorber is insensitive to oblique incidence and polarization, achieving a $S_{11}$ value less than $-10$ dB from 1 to 20 GHz. The strain sensor is sensitive to structural deformation and can predict device safety, while the energy conversion device can recycle waste EM energy. This work provides a novel strategy for developing multifunctional EM materials, which have significant applications in EM protection, pollution management, and military camouflage.The article explores the development of MXene/TiO$_2$ composites through annealing treatment to enhance their electromagnetic (EM) properties. The study demonstrates that by adjusting the annealing temperature, the composites can achieve a balance between EM energy loss and reflection, exhibiting excellent EM absorption and shielding performance. The optimized composites are used to fabricate various EM devices, including an energy conversion device, a strain sensor, and an ultra-wideband (UWB) absorber. Numerical results show that the UWB absorber is insensitive to oblique incidence and polarization, achieving a $S_{11}$ value less than $-10$ dB from 1 to 20 GHz. The strain sensor is sensitive to structural deformation and can predict device safety, while the energy conversion device can recycle waste EM energy. This work provides a novel strategy for developing multifunctional EM materials, which have significant applications in EM protection, pollution management, and military camouflage.