How do I get my Aspire 5 to show a 4-digit PIN log on ?

There is a toggle button on your screen to only allow Windows Hello login (PIN), turn that off, and the option appears to allow a password login.

A Microsoft Windows Hello Login Personal Identification Number (PIN) has 4 digits, this link explains it:

https://www.dell.com/support/kbdoc/en-ph/000149166/windows-10-setting-up-and-using-the-microsoft-hello-pin-log-in

to change your PIN: logon to your Microsoft Account on another computer if you don't remember your password click on Forgot Password under the password bar and you will be presented with alternatives, read this link also:

https://support.microsoft.com/en-us/windows/reset-your-pin-when-you-aren-t-signed-in-to-windows-a386c519-3ab2-b873-1e9b-bb228a98b904

If nothing works and you know your Windows password, at the sign-in screen you can enter Safe Mode by keeping the SHIFT key pressed and click on Restart in the Start-Power menu. Navigate to Troubleshoot > Advanced Options > Startup Settings and restart your PC. Select "Enable Safe Mode". You should create a new Windows Account in Safe Mode: Control Panel -->Admin Tools --> Computer Management --> Local Users groups and choose "New User" from the Action menu.

If you forgot your password you need a Recovery USB Flash drive to boot from and then navigate to Safe Mode this won't require a password. If you don't have a USB recovery drive, borrow one from someone that has the same Windows version.