SharePoint Online – BLANKINTERNET#0 Publishing Portal and Modern Pages

Short answer: B – not A.

Option A cannot be considered valid a site created based on BLANKINTERNET#0 does not support contemporary pages within the same site therefore, it is not possible to migrate classic Publishing Pages to Modern Pages gradually. The quote is still valid since publishing portals are intentionally not included into group connection and modern pages exclusion. There are no constraints regarding adding a Site Pages library into such a site and creating pages there, however, this will lead you off the official route and you will have all the expected issues the classic master page and chrome will control the navigation there, modern page components will expect modern site, etc.

So option B represents the official way of modernizing your site: creation of a new Communication Site >> migrating of the content >> retiring of the classic portal.

Two dates that should be considered separately since they often get confused

March 1, 2027 won't affect your existing site. It will prevent creating new classic publishing sites and activating the publishing feature. The only aspect to pay attention to: from that day it will be impossible to create a parallel classic site for the purposes of migration.

October 1, 2028 will make existing classic pages read-only. Your site will still work, pages will still be available, however, it will be impossible to edit them. This is a "plan it now" timeline, not an emergency.

With regard to SPFx + .NET 4.8 backend of your site: Web parts will be transferred "as is" if they are designed for modern pages; otherwise, web parts used on classic pages work differently, thus, check supportedHosts in your manifest.

.NET Framework 4.8 API is not influenced by the dates listed above. However, it still may require a separate investigation: if it uses SharePoint app-only/ACS authentication, it was fully retired in April 2026 and should be replaced by Entra ID application. Not related to publishing deprecation, however, tends to show up in the same period.

One more point, there is no need to perform a cutover. A common solution is creation of a new Communication Site and gradual migration of the most popular sections followed by redirections from the classic portal.