The discovery of Hafnia-based ferroelectric materials made ferroelectric field-effect transistor (FeFET) a more promising nonvolatile memory device than ever. Compared to the perovskite-based ferroelectrics, it could have a larger coercive field, better compatibility with CMOS fabrication, and good scalability. The importance of shrinking down FeFET cannot be overemphasized in the same manner as the CMOS. However, scaling down devices results in device-to-device variation. In the case of FeFET, the deposited ferroelectric layer possesses polarization variation (PV) induced by its crystallinity, whereby FeFET suffers from performance variation. Hence, it is critical to assess its influence quantitatively to utilize the FeFET for storage or compute-in-memory applications. In this review, recent trend and progress of the performance variation on the FeFET are surveyed. First, we present the impact of PV on three-dimensional (3D) NAND FeFET and 3D AND FeFET. In addition, to show its capability for compute-in-memory application, the inference accuracy is discussed under the structure. Second, the Voronoi diagram is introduced to model the different sizes and shapes of ferroelectric grains. Third, a comparative study of the device variability by different sources is investigated under the 28 nm to 7 nm technology node. Last, a machine learning-aided methodology to analyze the variability of FeFET based on the metrology results is proposed.