I think I didn't explain myself correctly. The photo was deleted from the drive, which makes me assume that there should be no trace of it in the Lightroom Classic backup, and yet it tells me that it may be a copy.
Anyway, when accessing the LrC cat (two Lightroom Catalog.Ircat and Lightroom Catalog-v10.Ircat appear) with the same size (1.58 MB) and the same date (April 9, 2021). The first took place at 11:24 and the second at 11:39.
As a solution, I have chosen to change the registration number of the photo _DSC6022.ARW to another that was not in the catalog and I have been able to import it. When I put the original number back, it appears as _DSC6022-2.ARW.
It's not orthodox, I imagine, but at least I've solved the problem for now.
Any comments on this will be welcome.
Thank you for your attention and my apologies for my bad English.
Very cordially
Daniel
The photo was deleted from the drive, which makes me assume that there should be no trace of it in the Lightroom Classic backup, and yet it tells me that it may be a copy.
If you deleted the photo via your operating system, then the above statement is incorrect. The knowledge of the file is still in the Lightroom Classic database, and that's why LrC still thinks it exists, and that's why importing it again will result in LrC telling you this is a copy.
As stated above, IMPORTING is not the solution. Simply copying the photo (using your operating system) to the folder where the original was stored is the solution. No renaming needed.
And I disagree that you have solved the problem. Especially for anyone else reading along who may have the same problem, do NOT import the file again. The photo is now in the database twice, once with whatever edits you applied originally and with whatever metadata you applied originally, and a new unedited copy with no user-provided metadata, that you just imported. Importing the photo again as you did causes confusion by having the photo appear in two different places in your catalog, two different edits with two different metadata in your catalog.