Currently, the SFTP connector in Logic Apps has been deprecated in the Designer, so its trigger and actions cannot be selected from the connectors list.
It is still supported in run time, however, so existing Logic Apps using the SFTP connector have not been affected.
If you want to create a connection via SFTP, you will need to manually create a connection to the old connector, using an ARM call, then edit your Logic App definition using Code View for the actions you want.
Below are the steps to do so.
1. Open any Logic App in your browser to collect the Bearer token.
Click on F12 > Network tab
On the left navigation pane, under "Name", search for an entry that begins with "runs?..."
In the "Headers" tab, scroll down to "Request Headers, and copy-paste the value of the Authorization key.
It will look like "Bearer <string of characters>"
2. Use Postman to create an ARM call to creating a connection to the SFTP connector.
Enter the following details in the Postman Request