Additional SQL Server features and topics not covered by specific categories
I am not aware of any documented setting that controls the date/time format used in built-in SQL Server Agent notification emails. The Microsoft documentation for SQL Server Agent mail and alert configuration does not appear to mention a configurable timestamp format.
If the US format is causing operational issues, a possible workaround would be to replace the built-in SQL Server Agent notifications with custom notifications sent through Database Mail, where the message content and date formatting can be controlled by your own T-SQL logic.
Since you are seeing UK formatting on SQL Server 2017 and US formatting on SQL Server 2022, it may also be worth checking whether this behavior changes after applying the latest SQL Server 2022 CU. If the behavior persists across fully patched SQL Server 2022 instances, it could indicate a product change or regression rather than a configuration issue.