> `remove_signal_handler()` should do nothing if `sys.is_finalizing()` is true.

I dislike this option.

If you want to use sys.is_finalizing(), I would prefer to modify _UnixSelectorEventLoop.close() to not try to remove signal handler if close() has been called too late during Python finalization. But I also expect a warning in this case, not hide bugs silently.

If you reach this case, close() has probably been called by BaseEventLoop.__del__().