I'm wondering whether this Epson L550 series can be linked or connected to a fax line?
Yes, the device can be used with a fax line because it has a built-in modem used for Fax sending and receiving. I recommend checking the official website of the product to download the PDF file. There are user guides and instructions on how to properly set up the device with a fax line.
Support page: https://www.epson.eu/ix/en/viewcon/corporatesite/products/mainunits/support/11856