Yes, you can connect to Excel files in SharePoint. To find the filepath, open an Internet Explorer browser - it must be Microsoft Internet Explorer, this does not work in Chrome or any other browser. Navigate to the Sharepoint folder that contains your file. Under All Documents, select "View in File Explorer" (this will not be available in any browser other than Internet Explorer). This will open Windows Explorer. In the filepath it will show something like https://companyname.sharepoint.com > site > subsite > folder > subfolder. Your path may be different depending on your company's configuration, but the syntax will be similar. The path for the Input Data tool will be:
//companyname.sharepoint.com/site/subsite/folder/subfolder.../filename.xlsx (dropping "https:" and adding a "/" in place of the " > "
It may be easier to copy the path from Windows Explorer and clean up the path in the Input Data tool.
To get the workflow to connect, you may need to be actively logged into your company's SharePoint site any time you run the workflow, especially if your company uses Single Sign On (very common). Once it connects you should be able to select the sheet and input your data.