I’m testing the SFTP Connector SuiteApp and came across this limitation below. Is this true? So we can’t send ABA files or any other files with different extensions?

You should be able to send ABA via SFTP Connector SuiteApp, I managed to do it before. You would need to test the connection with your bank anyway, it does not always work with all banks

Thank you. That's a relief.

Yes, ABA files are just text files and will work with SFTP. Where you may hit a snag is if your bank requires encrypted files or a fixed IP address.