I'm not sure if I understand you correctly, but if you have multiple catalogs, and want an option in the import dialog to choose what catalog to import to, I suggest that you open LrC with the catalog you want for that particular import. LrC can only have one catalog open at a time, and one catalog isn't aware of any other catalogs you might have.
Or even better, merge all your catalogs into one. Having multiple catalogs will lead to confusion and clutter.
With only one catalog, all your work is in one place, there is no need to relaunch to open a different catalog, and you don't have to remember what images are in what catalog.
If this is not the issue, please provide more details about what you want to be able to do.
As is, Lightroom Classic are using absolute paths. That meaning a file is placer at at specefic location. But when working with file systems you can use relative paths, ie. The location of the catalog file and work from there. It's like sessions in Capture One.
But currently Lightroom does not support this, that's why I suggest it as an idea.
This will in general make it simpler to move catalogs from one drive to another, and reopen them again in the new location, with out having to "re finding" the folders, if needed.
Working with one large catalog, is not optimal when ie. working on client/project work. Second large archives are slow, and for many different reasons, I prefer to have the organization of client work in my file system, not in Lightroom.
My personal pictures are en one large catalog established in Lightroom 2 🙂
You can move a catalog to a different drive, and it will still work perfectly, there will be no missing files or folders because of the move. That's how absolute paths work.
If you are sending edited files to clients along with a catalog, you can right click the client folder and choose Export this folder as a catalog. This will also eliminate the need for having multiple catalogs.
And large catalogs will not slow LrC down. I have seen reports from users having 500,000 or more photos in the catalog without speed issues.
I will not only be moving the catalog but also the images and the I have to remap the images afterwords, due to the absolute path would now be pointing at the old file position.
If it was a relative position like "catalog-path/images" then the location would still work.
The way my workflow is, are that I work on my active files on my Maschine and when they have been developed and delivered I will move them to an external drive.
I am not sending my catalog to the client.
I just wan't to be able to have one folder, with my catalog and the images, that I can move where ever I want, that the images, would still be "located" and ready to work on when I open them catalog.
LrC DOES support relative paths, but in order to leverage that the images have to be stored within the catalog folder with the parent folder of the images at the same root level as the catalog file. If setup correctly then you can simply move/copy that catalog folder to a different drive or system (even from Mac to Windows or vice versa) and there'll be no need to relink the images to the catalog.
No settings needed. LrC will automatically use the relative path if the folder containing the images is stored inside the catalog folder at the same root level as the .lrcat database file.
Does that mean, that the .lrcat file has to be in the same folder than the raw? Or is it one masterfolder and I can within the masterfolder two folders like "catalogue" & "raw"?
No, for this to work you can't have one folder containing the catalog and a separate folder containing the images.....both the .lrcat catalog file and the folder(s) containing the images must be within the same master folder.