Hi, @James Birchall Thanks for posting the question
If you do not have an app directly using 2014-04-01 API and if you only have " an Azure SQL database that accesses using .NET 4.8 linq to entities." then you are fine with this retirement.
keep up to the latest .NET SDK is enough.
Microsoft sent alert email to all the customers who registered for Microsoft.SQL.
you don't need to run any query unless you want to check any activity log on the email sent.
Please let me know if you have any additional questions.
Regards
Geetha