Can't Open Catalog on new laptop

I bought a new laptop recently.  I've downloaded Lightroom Classic and am trying to link it with my existing catalog.  I keep the catalog and photo library on an external drive and that has always worked well for me.  The version of LRC with which I saved the catalog is the same version that I am trying to open it with.  When I find the folder that the catalog is saved in, Lightroom can't find the file.  It doesn't recognize it as an lrcat file.  But if I go straight to the actual file on my external drive, everything is there and looks fine.  What am I not doing right?