I agree with @Drabslab. How to communicate the EOL of software is best thought of before platforms end, tools become unavailable or whatever reason there is for not being able to make an update to the software in question anymore. It is easy to drop a popup in any software when certain requirements are met. The simple existence of an eol-webpage with a certain code, could throw a predefined message about the EOL of the software, with a link for more information.