Is This Real?

For High School I know there isn't anything.

You can score a bunny statue for excellence while in class, but that might be it.

I talked about university, if I wasn’t clear.?

The diploma sometimes takes a few sim hours to appear in the sim's inventory after graduation. In my experience it goes into the sim inventory and not the household inventory but that may be different if you have to move out of student housing after graduation.

Ok, what about after graduation interactions or reactions?

You do get a notification (if memory serves) that the diploma will appear in their personal inventory. It's usually a few hours after the graduation ceremony.
As for after graduation interactions, none that I've noticed.

You will get the cert as well as a photo. And the salary scale is awesome!

Usually the diploma shows up in the sim's inventory after the graduation ceremony. I noticed that if you switch households though, you won't get the diploma.

Hey by the way do diplomas look different based on the sim's specific GPA/grades?

The diploma appears around 5 or 6 pm on the day of graduation.

The diploma, (and a photo if your Sim chooses to go to the graduation ceremony) will show up in your Sim's inventory.
HOWEVER here's a small warning: If you put them on a wall and then save the lot or share it on the gallery, the next owner cannnot delete the image or diploma without cheats since it "doesn't belong to them".

So if you plan on uploading or saving a house after graduation, put the picture and diploma back in your Sim's inventory before doing so.