before modifying your applications, I would consider creating a more detailed plan about what you need and how to achieve it.
My first two questions would be, about how difficult it would be to have your application whitelisted by their existing IP. Maybe that is simpler to your relatively low number off apps than adding a new feature to have less IPs?
If you want to scale and also use this as a manual process, I would consider using Azure automation or an existing marketplace solution. A process with scale could be to have your apps drop the files in a pre-defined location (storage account) you can control and than have Azure automation check for new files and transfer them.
SFTP - SSH connector: https://learn.microsoft.com/en-us/connectors/sftpwithssh/
SFTP in Azure Logic Apps: https://learn.microsoft.com/en-us/azure/connectors/connectors-sftp-ssh?tabs=consumption
Azure Automation: https://learn.microsoft.com/en-us/azure/automation/overview
SSH to storage account: https://learn.microsoft.com/en-us/azure/storage/blobs/secure-file-transfer-protocol-support-how-to?tabs=azure-portal
You can also check the Azure marketplace and identify an existing solution by using new resource and search for sftp, I would see a few fitting solutions. Maybe use them initially while you learn and replace them later (or enjoy a SaaS aspect).
Examples that might fit:
Both offers do have a solution in the marketplace like "SFTPGo - SFTP, HTTP/S, FTP/S to Azure Blob Storage" or "
SFTP Gateway for Azure - SFTP to Blob storage".