If you need steps for switching from Basic Authentication to Modern Authentication, please refer to the article How do I switch from Microsoft's Basic Authentication to Modern Authentication (GraphAPI)? .

Here is a section from the article for those not ready to upgrade to Retain 4.11 and/or switch to Modern Authentication.

We highly recommend upgrading to Retain version 4.11.  If you are unable to upgrade to Retain 4.11 at this time and Microsoft has turned off Basic Authentication for your tenant, please follow the steps in the Microsoft article 'Basic Authentication Deprecation in Exchange Online - September 2022 Update' .   Look for the section:
Re-Enabling Basic for protocols (available since October 1)
You will see:
Starting October 1, the diagnostic will only allow you to re-enable basic auth for a protocol that it was disabled for.
If you did not opt-out during September, and we disabled basic for a protocol you later realize you need, you can use this to re-enable it.
Following the instructions from Microsoft will re-enable Basic Authentication until January 1st.  You will need to upgrade to Retain 4.11 and apply the steps in this article to switch to Modern Authentication prior to January 1st to avoid any disruption in service to your Retain environment.