Please use "DRM Info" app (available on Google Play Store) to check your real Widevine's level (L1 or L3):
- If you have Widevine L1 => Clear "All app data" of the Netflix app in phone's settings.
- If you have Widevine L3 => Nothing can be done to get Widevine L1 back on your device... (and a low chance from Xiaomi to give, in future, a fix for that...)