File -> Apps Information field -> create a filter

File β†’ Apps Information field

how can I create a filter based on the date a file was added to NextCloud, rather than changing it?

Maybe I’m the only one but I can’t understand what you mean at all based on your information! I’m probably just a little slow-witted, but please have compassion and explain your concerns in a way that people like me can understand it too.
And what has this to do with groupfolders?

Much luck,