ios – Where is photos.sqlite-shm

I am trying to sync my Mac (macOS 11.2.3) “Pictures” folder with my NAS using Synology Drive. I receive an error message stating that photos.sqlite-shm cannot be synced due to missing access rights or because the file is in use.

However, I cannot even find this file. What is it and where is it? It sounds like it has something to do with iOS. Thank you!