As of now, Microsoft Forms does not allow users to add an attachment field. Is a way to setup PowerApp to have the end user to submit an attachment (without using a data source [Sharepoint, CDS, or other]) and have Flow to send the email with the attachment?
They recently announced they will be adding in the attachment feature in Forms soon..not sure when and not sure if that will just be for the Pro version.
You can do that in PowerApps without using SharePoint using the Add picture under the Media section. I believe Shane has a video on this. I prefer the SharePoint method (even if you just delete it afterwards) because it is good for any trouble shooting but you can use the Add Picture, select files and then send them attachment them in PowerApps and send the email or you can send it over to Flow and do it there.