Teardown videos have concluded that the M2 MacBook Air 256GB comes with a single NAND chip of 256GB instead of two 128GB chips, which Apple previously used in base models of MacBooks.
Same M2 MacBook Air model with more internal storage has two NAND chips instead of one.
Single NAND chip might slow down the performance while copying large files, multitasking or performing any task that’s enough to max out 8GB of its RAM.