ramk It seems to me that the app is not allowed or able to create this folder in GrapheneOS and that might be the reason for freezing.
It should be allowed to create image files in that directory, even without having any specific permissions granted to it.
If you open the Flickr app log file (Settings app -> Apps -> Flickr -> Show log file), does it say anything that might indicate the cause? Look especially at the logs from the exact seconds where you experiences the freeze.
Other than that you can also try to clear all cache and data for the app.
From what app store is the app installed?