Lightroom Classic cannot locate old CR2 files

I want re-edit some photographs from a catalog that I have finished and archived around October 2014 (shot with 6D Mark I).

I want to edit from my previously edited settings.

I restore the catalog on my current PC.

I open it and it gets updates for current Lightroom Classic version (12.3) .

All pictures show the question mark sign as the raw files are not in the same location anymore. Though they are in the same location relatively to the catalog file... but so far things (don't) work in a way that was expected.

I click on the question mark sign then on "Locate" to open the "Locate" dialog.

The only "Files of type:" option is "Supported Files", so that is what is selected.

The "Locate Missing Photo" dialog is pointing at the folder where my .CR2 files from 2014.

(In theory at this point, I would simply select one file and all the other photographs from that catalog would be located again since they are all in the same subfolder.)

BUT: the folder appears empty in the "Locate" dialog.

So I cannot select the file.

I trying entering the file name manually in the "File name:" field (with and without the ".CR2" extension). The dialog still can find the files.

More tests:

- I cannot import of the files to the catalog because the "Import" feature detects that the files are already present in the catalog.

- I can import the files to a brand new catalog (but is NOT what I want to do) ... which make me think that the issue is on Lightroom's side and not on the files' side...