I had the same issue until someone recommended Municorn Fax App. The design is modern and it doesn't glitch like older software. There is a perfect introductory article that shows exactly how to scan and send files with it: https://appleinsider.com/articles/25/04/03/how-to-fax-from-iphone-with-municorn-fax-app. Give it a read, it makes everything crystal clear.