This is usually caused by a security setting in your web browser or a Windows account preference that forces Windows Hello authentication for saved passwords. You could disable this specifically for your browser so that it autofills your passwords without asking for a PIN every time, while still keeping your PIN for logging into your computer.
If you use Google Chrome, open the browser and click the three dots in the top right corner to select Settings. From the left sidebar, click on Autofill and passwords and then select Google Password Manager. Click on Settings on the left side and find the option labeled Use Windows Hello when filling passwords. Toggle this switch to the off position. You will be prompted to enter your PIN one final time to confirm this change. Once disabled, Chrome will fill in your website passwords automatically without triggering the Windows Security PIN box.
For Microsoft Edge, the process is similar. Open Edge and go to Settings by clicking the three dots in the corner. Navigate to Profiles and then select Passwords. Look for a setting titled Password health or a similar section that contains an option for Prompt for the device sign-in options before viewing or filling website password. Ensure this is turned off. If you see a setting for a custom primary password instead of the device PIN, make sure that is also disabled if you do not want any secondary prompts.
If the prompts continue across multiple browsers or apps, you may need to adjust a global Windows setting that restricts how you sign into Microsoft-related services. Open the Windows Settings app and go to Accounts then Sign-in options. Scroll down to the Additional settings section and find the option that says For improved security, only allow Windows Hello sign-in for Microsoft accounts on this device. Turning this toggle off should stop Windows from forcing you to use Windows Hello (PIN or biometrics) for web-based Microsoft account logins, allowing you to use your standard account password instead.
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hth
Marcin