Thanks for your question.
Try opening an Azure portal from different browser and check that the resource exists in your Azure subscription. You can do this by logging into the Azure portal, selecting the appropriate subscription and resource group, and verifying that the resource is listed.
Please follow “Resolve errors for resource not found” document to resolve such errors.
Resource not found errors - Azure Resource Manager | Microsoft Learn
You can also check the MySQL server using PowerShell command. Please find below-
Get MySql server by resource group and server name
And, CLI command to Get the details of a server.
az mysql server show- https://learn.microsoft.com/en-us/cli/azure/mysql/server?view=azure-cli-latest#az-mysql-server-show-examples
Let us know if this helps!