Threat actors monitor for newly disclosed vulnerabilities and actively scan the internet for unpatched SharePoint installations, often within hours of a CVE going public. A SharePoint farm is a large attack surface on its own, IIS, .NET, the search service, the user profile service, plus whatever custom solutions have been layered on over the years. Every one of those is now a standing target with no fix coming.

Compliance is the other side of this. HIPAA, SOC 2, PCI DSS, and similar frameworks generally treat unsupported production software as an audit finding. Several cyber insurance carriers have already started writing policy exclusions for incidents traced back to end-of-life software. If your SharePoint environment is central to how your business handles documents, workflows, or client data, this is no longer just an IT conversation.

If you're still on 2016 or 2019, the priority list looks like this:

1. Get visibility fast. Run an assessment of your current farm, what's on it, what depends on it, and what breaks if it goes down.
2. Decide your path. Broadly, that's SharePoint Online in Microsoft 365, SharePoint Server Subscription Edition if you need to stay on-premises, or a hybrid of the two.
3. Reduce exposure while you plan. Restrict external access where you can, and harden configurations in the meantime.
4. Get the licensing and timeline sorted. Migrations typically run 6 to 18 months depending on complexity, so the sooner this starts, the more control you have over the process.