Your screenshot shows that, at some point, you selected the option to Prompt for the custom primary password before filling website password. The Learn more link next to it explains what this means.As soon as this option is selected, you would have been asked to confirm your Windows authentication, e.g. by entering your Windows password or PIN:
Having done so, this dialogue appears:
This is the password you're now being asked for. As the article referred to says,
"There is no way to recover your custom password if you lose one; hence it is***strongly recommended that you turn on Sync,***at least for your data that you don’t want to risk losing access to.
"In case you forget your custom password, you'll need to delete your profile, clear all app data on your computer and again sign in and turn on sync for your browser."