Hey there Valevan,
Thanks for reaching out to the Apple Support Communities.
If you're seeing duplicate photos in the Photos app on your Mac, you should be able to merge the photos and have them remain where they are located in the library and album. For more information, check out this link here: Remove duplicate photos in Photos on Mac - Apple Support
1. In the Photos app
on your Mac, click Duplicates in the sidebar.
2. Select the duplicates you want to merge.
You can select individual items in a single row and merge them or select multiple rows of duplicates and merge them all at once. A single original photo or video is kept from the selection in a row and other duplicates are deleted.
3. Click Merge [number] Duplicates.
One original photo or video appears where the selected duplicates were located in your library. Deleted duplicates appear in the Recently Deleted album where you can recover or permanently delete them.
Let us know if that's able to help.
Take care.