Look at the article https://proconnect.intuit.com/community/general-login/help/when-opening-lacerte-the-sign-in-screen-i...

I think both @Intuit_Al  and the article could use some minor editing:

When attempting to sign in to your Lacerte Tax software the Sign In screen does not show the fields to enter your user name and password or the fields are present but you cannot type in your sign-in information.

Follow the steps below:

1. Close Lacerte.
2. Open Windows File Explorer.
3. From This PC choose Windows C:
4. Open the ##Tax folder where ## is the year (Ex. 20TAX , 19TAX).
5. Open the w##tax.exe.config file. (Ex. w20tax.exe.config , w19tax.exe.config) If asked what program you want to open the file in, choose Notepad.
6. Find the <appSettings> section.
7. Locate the line below,
   • <!--<add key="Intuit.Spc.Authorization.EmbeddedWebBrowserImplementation" value="Standard"/>-->
8. Remove <!-- and --> from the beginning and end of the line so it looks like this,
   • <add key="Intuit.Spc.Authorization.EmbeddedWebBrowserImplementation" value="Standard"/>
9. From the File menu choose Exit. When prompted to save choose Yes.
10. Open Lacerte and try to sign in again.

Note: These steps must be performed for each year of the program you are experiencing this issue and will need to be performed after each update.