Describe the issue:
In versions less than 2025.12.0, passing keyword arguments to da.to_zarr would apply to writes, however now they only apply when creating the zarr store which breaks existing code.

Minimal Complete Verifiable Example:

import dask.array as da
import zarr

# following code works with "dask<2025.12.0", but fails with "dask==2025.12.0"
da.to_zarr(
    arr=da.random.random((100, 100), chunks=(10, 10)),
    url="test.zarr",
    compute=True,
    dimension_separator="/",
)
assert zarr.open("test.zarr", mode="r")._dimension_separator == '/'

Anything else we need to know?:

Environment:

• Dask version: 2025.12.0
• Python version: 3.12
• Operating System: Mac
• Install method: pip