Hi @Vikas Neekhra , welcome to Microsoft Q&A forum.
Using REST APIs, I think we don't have the way to list the databases using SKU as filter but we can use PowerShell commandlet like below to get the list of databases by providing the filters:
Get-AzSqlDatabase -ServerName <Name of Server> -ResourceGroupName <Name of Resource groups> | Where-Object {$_.SkuName -like 'GP_Gen5' -and $_.Edition -like 'GeneralPurpose'}
Please let me know if this is helpful or else we can discuss further.