Windows does not implement the "61th second", e.g. "23:59:60" system time , so the risk of application breakage is mitigated.
It assumes that the external (non-Windows-based) time servers will handle the issue, and the highest-stratum NTP servers never run Windows anyway.
If Windows is configured to sync with a time source (using NTP), and that time source has the leap second applied, the 1-second discrepancy will be detected and corrected just like normal clock drift.
Extra 1-second clock drift during a single day should be barely detectable, and will not cause any issues with Password Manager.