$ cat >sim101_1.py <<'# EOF'
isinstance(f"{(lambda: 0)}", int) or isinstance(f"{(lambda: 0)}", str)
isinstance(f"{0:{(lambda: 0)}}", int) or isinstance(f"{0:{(lambda: 0)}}", str)
isinstance(f"{0:\x22}", int) or isinstance(f"{0:\x22}", str)
isinstance(f"{0:\x7b}", int) or isinstance(f"{0:\x7b}", str)
# EOF

$ ruff --isolated check sim101_1.py --select SIM101 --unsafe-fixes --diff 2>&1 | grep error:
error: Fix introduced a syntax error. Reverting all changes.

$ cat >sim101_2.py <<'# EOF'
from datetime import datetime
d = datetime.min
class OddMeta(type):
    def __instancecheck__(self, instance):
        return len(instance) % 2
class Odd(metaclass=OddMeta): pass
print(isinstance(f"{d:\x7d}", int) or isinstance(f"{d:\x7d}", Odd))
print(isinstance(f"{d:\x7b \x7d}", int) or isinstance(f"{d:\x7b \x7d}", Odd))
# EOF

$ python sim101_2.py
True
True

$ ruff --isolated check sim101_2.py --select SIM101 --unsafe-fixes --fix
Found 2 errors (2 fixed, 0 remaining).

$ python sim101_2.py
False
False