Just following up after having done more experimentation. Rolling back to prior saves (including saves from prior days, from before the 9/24/25 update, and from prior in-game days) and then going through the graduation has not solved the problem. The situation remains exactly the same as before: as soon as the graduating Sim in DU completes graduation, the graduation photo generates in their inventory as blank.
To see if I could see anything specifically happening at the moment of generation, I had a graduating Sim's inventory open to the Sim-crafted Photographs category and the graduation photo sub-category at the moment of generation. I noticed that the second the graduation photo spawns into the inventory, it generates as black. But this only lasts for a fraction of a second, and then it turns white (as described previously). Not sure if that is relevant but figured I would mention it.
In terms of additional information for my save, I have the following packs and kits:
EPs: Businesses & Hobbies, City Living, Discover University, Eco Lifestyle, Enchanted by Nature, Get Famous, Get Together, Get to Work, Island Living, Seasons, Snowy Escape
GPs: Jungle Adventure, Outdoor Retreat, StrangerVille
SPs: Bowling Night, Crystal Creations, Home Chef Hustle, Luxury Party, My First Pet, Romantic Garden
Kits: Artist Studio, Blooming Rooms, Book Nook, Casanova Cave, Comfy Gamer, Cozy Bistro, Cozy Kitsch, Desert Luxe, Fashion Street, Grange Mudroom, Greenhouse Haven, Modern Luxe, Refined Living Room, Restoration Workshop, Riviera Retreat, Secret Sanctuary, Simtimates Collection
Free: Holiday Celebration
Also not sure if relevant, but the problem started after I installed Eco Lifestyle and Enchanted by Nature. Other than those and some Kits, I have not added anything to be game in the intervening time between when the graduation photos worked in this save with these Sims and now.