List - Test2
Customer: Lookup field to Customers
Customer Exists: Choice Yes or No
Library - CustomerFolders
Does the flow run- when an item is created, or modified, or when a condition is met? You'll need the right trigger and maybe a trigger condition. I set it to manually start and you enter the ID.
Create the content for the file. We'll use this to create a text file.
Create a variable for the folder path - /DocumentLibraryName/CustomerName
Use a condition to see if the customer exists.
Check to see if the Customer Exists = Yes
If yes, create the file.
Otherwise, create the folder, then create the file in the new folder.
Hopefully this is enough to get you started. There is a great Power Automate community here. https://powerusers.microsoft.com/t5/Forums/ct-p/FL_Comm_Forums