As you aware as part of retirement, we'll no longer support creating new Single Server instances from the Azure portal. Additionally, starting March 19, 2024 you'll no longer be able to create new Azure Database for MySQL Single Server instances using Azure CLI.
But as mentioned in the FAQ document, if you still need to create Single Server instances to meet business continuity needs, you can submit an Azure support ticket with justification to create a single server, and the support team will likely take this forward to the product team.
Thank You.