How do I get the heat sink bracket off on the Mac Pro 2013 (trash can)?

I have a Mac Pro 2013 which I bought in 2018. I’ve read they are upgradeable (macsales.com has a video on how to do it). I bought a 12 core chip to replace the 6 core chip it came with. I tore the whole thing down and got to the heat sink retainer clip. Every video or website I’ve read (iFixIt has a text version, and there are several videos on YouTube including the OWC video) shows a total of 8 screws. Four outer screws, which I think are T8. And four inner screws. The four inner screws are not screws on my unit. They’re just round nubs. I’ve applied a little bit of pressure attempting to pry them loose but they won’t budge. I don’t want to get too rough with it because I don’t want to damage the board or the original CPU given it seems like Apple changed this to be not-upgradeable. What I’m a missing here? Was such a change made? Is it safe to pry until they pop off, or are they rivets and not designed to be removable? ![Photo of heat sink retainer clip showing the four inner fittings ][1]