The Short Version
Recent app updates broke Find My Phone and ECG on Pixel Watch 3 and 4, leaving both features completely unusable for multiple users.
A recent app update broke two of the most important features on the Pixel Watch 3 and 4: Find My Phone, which lets you ring your phone from your wrist, and ECG, which reads your heart's electrical activity to screen for irregular rhythms. Both now crash on launch, leaving them completely unusable. Google sells these watches partly on the promise of health tools that work when you need them. An ECG app that crashes is not a health feature.