The absolute last XP variant of Embedded POSReady 2009 ended yesterday and users have until to July to apply the last patches.
Counting this edition, Windows XP is the longest-lived version of Windows. There is still Windows XP software but Windows Embedded for Point of Service SP3 and XP#Embedded SP3 reached end-of-life in 2016, while support for Windows XP Home and Professional SP3 ended five years ago, on April 8, 2014.
POSReady 2009 allowed users to receive security updates on Windows XP Home and Professional SP3 through the use of a registry hack. Microsoft dissuaded users from doing this, stating that they "do not fully protect Windows XP customers" though no attempt was made to prevent users from using this hack. With POSReady reaching the end of support, the flow of these security updates is no more.
There is absolutely no reason on earth why anyone would be dumb enough to run Windows XP. Installing it is the software equivalent of putting Justin Beiber into a maximum security prison – only without the satisfaction of taking Beiber out of society.
Australian Department of Defence only migrated the last of their systems off of Windows XP in February 2019. We guess the Russians asked them to upgrade because they could not be bothered keeping that particular hacking skillset alive.