Photos App looking for original photo files

Hi! I have a recent problem with Photos app, likely to be linked with today's Sonoma update.

I have 3 libraries: 2 on my local drive (M3 MBP) and 1 one an external SSD. I've been using the Photos App for several year now and I always follow the same pattern: I dragged the photo file (raw+jpg) to the app but kept the original files on an external drive. The drive was not connected to my laptop and I was still able to edit my pic in the Photos app. As I understood, this was not necessary, as the pics dragged into Photos would be "incorporated" into the library file. I never had issues until today, when I suddenly get the message: "Photos cannot be opened if the original files associated with the photos are not available. The original photo "IMG_4926.JPG" is offline or cannot be found. Click on "Find original" to reconnect." If I attach my external SSD, everything is fine. But this is obviously not the way to go, I don't want to keep about 1TB of photos "duplicated" on my Mac (i.e. both in individual folders and the Photos App). Any idea?