Importation of a catalog does not import previous modifications of pictures

florencec46117915  wrote I just changed my computer and decided to create a new catalog, the previous one being "a bit" large.

No such thing as a catalog that is too large, or even "a bit" large. And it seems as if this misunderstanding on your part has caused you to do some unnecessary work, and then on top of that, it didn't work the way you thought it would and so now you have to do more work to fix it. I would recommend sticking with the one catalog, and if necessary, addressing whatever problems you are seeing in the one catalog.

I exported from the old one a catalog with a set of pictures from my last holidays, some pictures already developed and others not yet. If I open this catalog, everything is OK (developed pictures are still developed and tagged). However when I import this catalog in the new one (where I already imported the raw files, in the exact same location) the modifications, stars and tagged are not imported. How can I manage this ?

These words are not terribly explanatory. It would help if you told us, step-by-step, using the exact name of each step/command/function in Lightroom, and not a verbal description of the process. Nevertheless, you have all the symptoms of doing something wrong, most likely importing the photos into the new catalog using the Import button, or the menu command File->Import Photos and Videos...

If you use ‘import from another catalog’, then you should not also import the images directly.