Per the discussions yielded in Policy Change Proposal: "End of Standard Support" for ESM releases is effectively the "Not Supported" date for a release on Ask Ubuntu and 30 days of voting done, there was overwhelming support 39 to 8 to amend the Help Center and Close Vote reasons to include the move verbose definitions of "End of Standard Support" and "End of Life" (whichever comes first) as the date that support for a release goes away.
The Moderation team has already updated the Help Center's 'on topic' help page with this information and a link to the Releases page on the Ubuntu Wiki with the relevant dates.
We are waiting on the Community Management Team to edit the existing close reason to adjust for this change. The Community Managers have revised the close rule for "end of life" releases to include "end of standard support" as well, as well as update the close reason to the new format that StackExchange is using.
This is now in effect as of April 12, 2021. Any questions about a release that has reached its End of Standard Support date or its End of Life date, whichever of the two is the earlier date, will be offtopic when that date is reached.