Is there a configuration file for Photos, .ini or something else, to fiddle around with advanced settings? Or some other way to do that.
The stuff you're looking for would appear to live in...
This directory contains a data directory, which contains 2 database files. Those 2 files appear to be in SQLite format, and you should be able to open and edit them using an SQLite browser such as GUI Editor for SQLite Databases
Naturally the .bak file seems to be a backup of the other file. I'm not sure why, but presumably in the event that the photos app crashes, it will resort to using the backup. I would recommend having Photos closed when making changes to the database files. Be aware that any changes you make in the Photos app may also be overwritten if you make changes in the database browser afterwards. Just, generally speaking, don't have the database file and Photos app open at the same time.
Further background information: Elementary OS seems to use their own take on Shotwell photo viewer, and as such the configuration files live in the same place. This appears to be true of some other Elementary apps.