Support of EOS r6 .cr3 files in Lightrooom 5.7

That camera model is supported in Lightroom Classic 9.4, which as of today is the very latest release. Lightroom Classic, as well as ANY current version of Lightroom is only available by subscription. There is no update that will ever be available that will make the raw files from the camera compatible with Lightroom 5.7. However, Adobe provides a free DNG converter which is a standalone application that enables you to first convert the raw files to DNG files which would be compatible with older versions of Lightroom if you insist on staying with out of date software.