Overview

As of 11/15/2023, this is no longer an Identity Engine upgrade blocker.
This KB has been replaced with new telemetry.  If it is applicable would trigger reference to the article: 
https://support.okta.com/help/s/article/self-service-registration-read-only-bypass-progressive-profile
Note, additional Okta features may require reconfiguration or be disabled in order to complete the upgrade.

FF - ENG_SELF_SERVICE_REGISTRATION_READ_ONLY_BYPASS
Upgrade Eligibility: Fully Eligible

In classic, the Self-Service Registration was site-wide, with this feature flag the ability to allow end users to insert a "Read-Only" on account creation.

How does this blocker impact the upgrade to OIE?
No action needed to proceed with the upgrade, 
Note: The ability to write to a Read-only Attribute is not supported with OIE and will no longer function post-upgrade. There are no plans/roadmap of supporting this capability in the OIE framework due to the low customer adoption. 

How do I remediate this blocker?
If this is required, build an alternate solution using Okta Workflows and inline hooks prior to the upgrade

Impact when disabling the feature
There is no need to disable this feature. It will be turned off during the upgrade.

Is there additional training or information I can use to help me with this remediation?

Alternative Method for achieving ability to use a "Read-only" attribute in Self-Service Registration would require the usage of an inline Registration Hook And/OR Account Creation event hook; Either of these triggers could be configured in Okta Workflows.

High-Level steps to prepare a "read-only" attribute for self-service registration upgrade:
1: Create a new attribute with "Read/Write" user access;
2: Replace the current attribute in the Self-Service Registration policy.
3: Create a Registration/Event hook that will copy the new attribute "read/write" value to the original "read-only"