Calibre does not show the covers of PDF files

Hello.
I have been using Calibre for several years without any problems, but now I have changed my PC and after installing it on the new PC, I see that every time I import a book in PDF format, the cover does not appear in the book details window. I have been looking at the options, but I can't see what needs to be changed for them to appear automatically, as they used to.
Please, can you help me?
Thank you