Hello Adan Turbo Fjert,
Thanks for posting your question. As we understand it, you seem to be seeing duplicated photos on your Mac. We understand wanting to look into this, and we're glad to help.
To clarify, is this happening with photos you download using Safari or similar apps, when you import photos from an iPhone or camera, or all of those?
Also, are you finding that photos automatically appear in the Pictures folder even if you save them elsewhere, like on your Desktop?
To check one possibly related setting, in the Photos app, click Photos > Preferences. Is "Copy items to the Photos library" checked here? Change preferences in Photos on Mac
"By default, Photos stores all imported photo and video files in the Photos library. To leave imported items in their current location outside of the library, deselect the “Copy items to the Photos library” checkbox. If photos are stored outside the library, they will not be automatically uploaded to iCloud Photos and available on all your devices. You must manually back them up to safe storage locations."
Best wishes.