I've a collection in LrC but no way to get a new to it??

If you are experienced with Bridge and you prefer it, that’s good…that will help you understand how it works in Lightroom Classic. Although it’s not exactly the same, it's similar enough. It's not any kind of “roulette” at all.

In Adobe Bridge, the Folders panel shows the location of the files in the folders on your computer. And the Collections panel in Bridge can show the same files in arbitrary lists that are not tied to the folders containing the files. In that way, the Collections panel in Bridge is like making playlists for music or video: Each playlist can be any form of organization you want, independent of their storage location. One advantage of collections is a file can exist in multiple collections for different purposes.

It’s mostly the same in Lightroom Classic: The Folders panel is where the images are stored, the Collections panel contains optional virtual lists of the same images organized any way you want.

I have all the projects pictures in a collection in LrC. Now, I wanted to edit one of the pictures in another app, Topaz Photo AI, and therefore I copied the picture to another folder, and then, after, trying to get that edited picture back to LcR, it didn't work. I just have to say: I never got the picture to LcR. WHAT is the way to get  picture edited outside LcR to the collection

By @tuomasvirtanen.fi

If you copied the image to another folder and edited it, was that copy made outside of Lightroom Classic, like on the desktop? If so, that means Lightroom Classic is not aware there is a copy, because Lightroom Classic doesn’t automatically track what happens out in the operating system. If I’m guessing right, what needs to be done is to import the edited copy into the same Lightroom Classic catalog. Then it will appear in the Folders panel. If you made the copy in the same folder as the original, that's where it will be in the Folders panel.

As a freshly imported image, it won’t be in any collections yet, so you will have to add the new image to the collection you want.

If instead you made a virtual copy in Lightroom Classic and sent that to Topaz, again a new file was created in the file system. I haven’t used Topaz but if it doesn’t return the new file to Lightroom Classic automatically, again it will need to be added to the catalog (imported).

Having to add it to the catalog is really the only thing that’s different than Bridge. That’s because the Lightroom Classic catalog is a database, while Bridge is a straight file browser. But the way Lightroom Classic isn’t unusual. It’s the same way video editing applications, page layout applications, and websites work: All of them keep track of files by using the files’ folder paths, and if a new file appears, it must be imported so that the software can track it too.

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.

<"moved from using the community">

In Lightroom-Classic you can add most other apps (Topaz, etc) as an External Editor.

The workflow is to select a photo in LrC library and [Edit In] > [Edit in the External Editor]. Then you [Save] the image in the external editor and the new file automatically appears in the LrC catalog.

There is no need to 'copy' a photo to another folder. By doing this you are opening the file in another app that is not linked to Lr-CLassic requiring you to Import the new photo to the LrC library.

https://lightroomkillertips.com/configuring-additional-external-editors/