I don't know from where you want to get the files. If you want to get from Sharepoint, using the get file action, you will only add the file returned by the action.
But if you have another places that you have to retrieve and you have the base64 data you must using the following pattern, to act as binary file in power automate;
{
"$content-type": "application/pdf", //type of the file
"$cotnent": "" //base64 of the file
}
using that in the compose it will be a binary file that you can include in the attachments of e-mail