Oracle Forms

Encryption of what; the Forms userid setting OR the WLS managed server username/password?
Of course the more obvious question would be, why would you want to turn either of them off?

Encryption Forms userid setting in config of formsweb.cfg

Are you trying to turn it off or on? If you are trying to turn it off, I would like to ask why?

i what to turn if off to test something and turn on again

We purposely do not offer much documentation on tinkering with this, however do provide instructions on how to enable it when upgrading since it is not enabled by default when upgrading. You can use that information to do the reverse. Keep in mind that on a new .4 installation you will not need to tinker with the Policies. You just need to make the setting change in the script. Refer to Step 2 in the Upgrade Guide here:
https://docs.oracle.com/en/middleware/developer-tools/forms/12.2.1.4/install-fnr/upgrading-oracle-forms.html#GUID-4140BE59-72A0-44E6-B100-000E88F9A5EB

-Dforms.userid.encryption.enabled=true

We normally set userid=@dbname in formsweb.cfg so that the DB name is automatically populated when a user starts a form. If this turned on what happens is that the encrypted value is entered in the UserName text box of the login screen. End Users usually are stumped at this point since they normally do not pay attention to the DB Name when logging in. That's why we turn it off.

@bill-cummins
Setting userid as you mentioned is not a good idea and is not the intended use for this parameter. Don't be surprised if at some point doing this stops working. This would not be addressed as a defect as it is not the intended way to use the parameter.
If you want a "default" Database you should set TWO_TASK (LOCAL on Windows) and instruct the users to leave the field blank. In version 12 you can add such text to the login dialog using the FORMS_LOGON_HINT environment variable. Here is an example (copied from the Forms New Features guide):
FORMS_LOGON_HINT=Username and password fields are case sensitive.
The message can be as long as 255 single-byte characters. More information about this and many other features in 12.2.1.4 can be found in the Tech paper mentioned. In the Documentation section of the page, click on "Forms 12c Supplemental Content"
https://www.oracle.com/application-development/technologies/forms/forms.html
In a future version, there is a planned enhancement to allow for hiding the Database field. This along with setting TWO_TASK (LOCAL on Windows) will help to avoid user confusion. For more complex or flexible options you should create your own custom logon dialog. Here an example I posted previously: