Release Updates affecting system access
Key Takeaway
Starting a test run turns a release update on in your org right away. The update stays on until you click "Disable Test Run". You can turn the test run on and off as often as needed until the Complete Steps By date.
Release updates are changes that Salesforce periodically releases to improve an org's performance, security, logic, and usability. Because release updates can also affect your existing customizations, admins review, test, and complete them in the Release Updates node in Setup before Salesforce enforces them.
Where release updates appear
Release updates appear in the Release Updates node in Setup. To open it, enter Release Updates in the Quick Find box.
Release updates are available in all editions and in both Lightning Experience and Salesforce Classic. They are not available in all orgs.
Release updates replaced the Critical Updates console and give more detail about upcoming changes. Release updates also replaced security alerts, so information about previously released security alerts is now in the Release Updates node.