Asklemmy

That's a nice theory but the dodecahedron was found in across a wide region of the western side of the empire and primarily in military graves. There's also the rarer icosahedron which didn't have large holes on the sides which really jumbles up theories. I'll give some interesting ideas for it's use I've heard.

Cryptography, when combined with a disc-like key it could be used like "move clockwise after every word" like this guy speculate https://youtu.be/vBDgmE3d0aw. Notable issue with this is that it's waaaay more complex to manufacture than required. You could make the first key with a hexagonal hole and the second key that slots into it. No dodecahedron required.

Craftsman proof of expertise, since it's very hard to manufacture it can be used as a proof you can make it. But then why was it found a lot in military graves?

Artillery calibration, by using the holes you could put down rocks at 200m, 300m and 400m marks and see which rocks fits exactly inside inside the view when the two holes line up in size. Hard to prove and there's no need to have such an extensive number of knobs on it to fulfill that purpose. Could save a lot of expensive metal by having it made of wood for example.

Knitting fingers, it's not very convenient and suuuper expensive for its purpose.

Weaved metal, more plausible than knitting but if this was the case we would see scratches or signs of use along the holes.

Religious artifact or recreation, this is the archaeological "we don't have anything better" explanation. Can be used as a fancy dice or for asking the gods or something. It only sounds plausible because we don't have anything better.

This is why it's still a mystery even though so many people have guessed, the knobs on every corner, difficulty to manufacture, cost, varying hole sizes and that it's found in military graves is very hard to put together. It's looking like we're going to need to find a non-existing manual for it's use.