Hello AA
Welcome to Microsoft Q&A Platform, thanks for posting your query here.
Based on the information you shared, it seems that you have received an email from Azure notifying you that Ubuntu 18.04 LTS will reach its end of standard support on May 31, 2023, and advising you to ensure that your VMs are on a supported operating system. However, you are unable to find any VMs using Ubuntu 18.04 on your subscription.
Please cross check once by logging into your subscription, and go to Virtual Machines, and under operating systems with Linux check the OS details.
If you do not see any VMs using Ubuntu 18.04, then you can be confident that you are not missing anything.
There could be a possibility that a Ubuntu VM might have been created and deleted recently and this notification was sent.
It is also possible that the email you received was sent in error or that it was intended for another Azure subscription. However, to be sure, you can contact Azure support to inquire about the email and confirm whether it was sent in error or if there is any other action you need to take.
Hope this helps.
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