$ cat >furb122_1.py <<'# EOF'
with open("furb122.txt", "w") as f:
    for char in "a", "b":
        f.write(char)
# EOF

$ ruff --isolated check --preview --select FURB122 furb122_1.py --unsafe-fixes --fix
Found 1 error (1 fixed, 0 remaining).

$ cat furb122_1.py
with open("furb122.txt", "w") as f:
    f.writelines("a", "b")

$ python furb122_1.py
Traceback (most recent call last):
  File "furb122_1.py", line 2, in <module>
    f.writelines("a", "b")
TypeError: _IOBase.writelines() takes exactly one argument (2 given)

$ cat >furb122_2.py <<'# EOF'
with open("furb122.txt", "w") as f:
    for char in "a", "b":
        f.write(f"{char}")
# EOF

$ ruff --isolated check --preview --select FURB122 furb122_2.py --unsafe-fixes --diff

error: Fix introduced a syntax error. Reverting all changes.

This indicates a bug in Ruff. If you could open an issue at:

    https://github.com/astral-sh/ruff/issues/new?title=%5BFix%20error%5D

...quoting the contents of `furb122_2.py`, the rule codes FURB122, along with the `pyproject.toml` settings and executed command, we'd be very appreciative!