To use autofill on Windows/Mac install Safe extension for your browser.
Open Options (Preferences on Mac) > Autofill to install the extension and to configure its authentication (auto-lock period and login with Windows Hello)
If autofill fails on some website, make sure:
- you have a card for this website in Safe database;
- this card has non-empty and correct Login, Password and Website fields;
- autofill for this card is enabled, and its fields have correct autofill attributes (click Autofill on the edit card window toolbar and check Use for Autofill checkbox and field attributes).