Okay, well luckily Power Automate already have an automated trigger for when files are moved to a folder.
I would use the "When a file is created", as moving the file to the folder will trigger it.
Now, I assume you have multiple files in that folder, and one of the issues is having the system recognize which file is the newest. I would apply metadata to the files in sharepoint for this. Create a property column and call it whatever you want, lets assume you call the column "Property Status".
Make sure the property column is a choice column, I would apply these two choices:
"Not Read" / "Read".
Create the flow using the trigger I mentioned, and apply the necessary actions in the flow. When you use the "Get files" command, make sure you apply the filter query expression as follows:
PropertyStatus eq 'Not Read'
Remember to set the default value of the column, to be "Not read" so that metadata is applied to the file, as soon as it is moved into the folder.
This ensures that only the documents the system has not read, is the ones you're asking it to find. Then do whatever, the flow needs to do and end the flow with a "Update file properties", and change the "Property Status" value from "Not read" to "Read". that way, everytime the flow runs, it dynamically filters all the documents that has already passed through the flow, and only gets the newest document.
I hope this makes sense, otherwise feel free to ask.
best regards - AndreasN