According to the new note on this page registrering a new ACS account is now being put behind a new security option.
We are still using ACS for some remote event receivers we build on SharePoint online. Webhooks don't offer the sync events. Will ACS continue to be a supported way of creating an ad-in or will this be deprecated in the near future?

Site collection admin is not able to register add-in with Azure ACS in AppRegNew.aspx by default unless explicitly allowed by the SharePoint tenant admin. For more information, see [Set-SPOTenant](https://learn.microsoft.com/en-us/powershell/module/sharepoint-online/set-spotenant#-siteownermanagelegacyserviceprincipalenabled).

Document Details

⚠ Do not edit this section. It is required for learn.microsoft.com ➟ GitHub issue linking.

• ID: 2be8c8d6-7ed2-1907-3038-49d8e1c92e8a
• Version Independent ID: a2adbe13-e625-3995-fded-fce6c4a701ac
• Content: Register SharePoint Add-ins
• Content Source: docs/sp-add-ins/register-sharepoint-add-ins.md
• Service: sharepoint
• GitHub Login: @VesaJuvonen
• Microsoft Alias: vesaj