The product lifecycles of all Microsoft software are published well in advance. Extended Security Updates should always be seen as a last resort if you can't update or migrate the server.
The new Arc method is intended to save customers money and has been communicated via various services since July. The base functions of Azure Arc are free and Microsoft can help provide the information and resource to get this deployed in your environment. The agent auto-updates and can actually simplify server management and security overall so has other optional benefits for legacy servers other than just ESU.
As mentioned, there is still the traditional method available if needed so I'd recommend speaking to your account team about the path your organisation wants to take wizball