If your company controls users’ or servers’ access to the internet through firewalls or allowlists, your IT department must add *.salesforce-setup.com to the company’s list of allowed domains. Salesforce Setup pages are now hosted on that domain.
Where: This change applies to Lightning Experience in all editions.
When: This change is applied on a rolling basis starting in Spring ’24. The change is first enabled in sandbox and non-production orgs, then in production orgs.
Allow the New Setup Domain to Ensure Access to Salesforce Setup Pages