• Since, you are using Azure AD B2C custom policies regarding ‘Signup and Signin’, which are working fine but when you are trying to decode the token received for information in it, you are not getting information on the ‘username’ of the signed in user, it is because of the ‘Validation Technical Profile’ section being executed before the ‘OutputClaimsTransformation’ section. Thus, when signing up with an Azure AD local user account, the ‘LocalAccountSignUpWithLogonEmail’ technical profile is used which includes ‘AAD-UserWriteUsingLogonEmail’ technical profile as the validation technical profile. As a result, if you check the ‘AAD-UserWriteUsingLogonEmail’ technical profile in your signin-signup policy, you can see that in your ‘PersistedClaim ClaimTypeReferenceId="displayName" DefaultValue="unknown" />’ is stated. As a result, since the validation technical profile runs before ‘OutputClaimTransformation’, you are getting the ‘DefaultValue’ of ‘unknown’.
Thus, the claims transformation profile should be as below in your signup-signin policy: -
<ClaimsTransformation Id="CreateDisplayNameFromFirstNameAndLastName" TransformationMethod="FormatStringMultipleClaims">
<InputClaims>
<InputClaim ClaimTypeReferenceId="givenName" TransformationClaimType="inputClaim1" />
<InputClaim ClaimTypeReferenceId="surName" TransformationClaimType="inputClaim2" />
</InputClaims>
<InputParameters>
<InputParameter Id="stringFormat" DataType="string" Value="{0} {1}" />
</InputParameters>
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="displayName" TransformationClaimType="outputClaim" />
</OutputClaims>
</ClaimsTransformation>
• Accordingly, ensure that the ‘Technical profile’ is also updated in your ‘LocalAccountSigninSignup’ custom policy as shown below and add ‘Validate-DisplayName’ technical profile as validation technical profile under ‘LocalAccountSignUpWithLogonEmail’ technical profile as mentioned below (in same order): -
<ValidationTechnicalProfiles>
<ValidationTechnicalProfile ReferenceId="Validate-DisplayName" />
<ValidationTechnicalProfile ReferenceId="AAD-UserWriteUsingLogonEmail" />
</ValidationTechnicalProfiles>

Thus, this would help you to resolve this issue of getting ‘unknown’ in the username. For more information, kindly refer the below link: -
https://docs.microsoft.com/en-us/answers/questions/713037/display-the-name-of-user-in-ad-b2c-instead-of-unkn.html