Google Photos API Limitation and Bug Report
Last year I still used Google Photos, but eventually said goodbye. One of the reasons was that one cannot organize the library in a meaningful way via external scripts. The web user interface lacks functionality, and I cannot write a script to help out.
The limitation is intentional by Google. The API can only work with media items, which were created by that API. This basically creates a few silos. Since 2019-05-08 there is a Ticket in the Google issue tracker where a user has complained about this not being possible.
And until today there are 143 people watching this issue, and tons of “+1” comments. I regularly get e-mails which just tell me that somebody has starred the issue or added yet another “+1” comment. There are even users who have started a project to organize their library and only afterwards found out that the permission model doesn't allow them to actually use it.
In the end it just makes clear what Google Photos is: It was a tool to gather tons of machine learning training data. And they want to organize everything by search alone. If that doesn't work for you, too bad.