How Lr 6 cataloq photos goes to Lr

Can you clarify the exact version of Lightroom you have installed. As @Rob_Cullen states, there are currently two different versions, and the instructions he provided are good if you have installed Lightroom Classic (LrC icon). But if you have installed the Lightroom desktop app (Lr icon), then you need to know that this is a very different app and does not have a function to upgrade a Lightroom Classic (or old Lightroom 6) catalog. Instead it has a "catalog migration" function which allows the contents of existing Lightroom Classic catalog (both the image files and the associated catalog metadata) to be imported into the Lightroom desktop app and uploaded to the Adobe cloud.

So before going any further, which Lightroom have you installed and secondly is that the version you intended to use? Because of the naming confusion, many users inadvertently installed the Lightroom desktop app when they actually wanted the Lightroom Classic app.

(There is no longer an app referred to as "Lightroom CC". )

Currently there is "Lightroom" [Lr],   and "Lightroom-Classic" [LrC].

When Upgrading from Lr6 [old perpetual version] to Lightroom-Classic, Classic may have missed the fact that you have a catalog from Lr6. (Might happen if the catalog is on an external disk.)

You do not have to "transfer photos" or do any Importing.

Exit out of Lightroom-Classic, Use Windows File Explorer to locate your Lr6 catalog and [Double-Click] on the .LRCAT catalog file. It should 'open' with LrC and give you the prompt to upgrade the catalog to be compatible with LrC v13.

You need to know where you catalog is located, and where you have made backups of the catalog.