It is true that there is no update for Lightroom 5.7.1 that will support your new camera. It is also true that there is a free DNG converter that will convert the raw files to the DNG format that will be compatible with that version. However, you will be robbing yourself of the many fine features that have been added to Lightroom Classic since Lightroom 5.7.1 that would enable you to get so much more from your raw images. Seems to me it would be such a shame for you to invest in a high quality camera and then use outdated software to process the images. Yes, it's $9.99/month in the US to subscribe to Lightroom and Photoshop. But for that subscription price you always have the latest versions of the software available to you.